Categorizing Patients With
Occupational Low Back Pain by
Use of the Quebec Task Force
Classification System Versus Pain
Pattern Classification Procedures:
Discriminant and Predictive Validity

Background and Purpose. Quebec Task Force Classification (QTFC) and
pain pattern classification (PPC) procedures, including centralization and
noncentralization, are common classification procedures. Classification
was done to estimate validity of data obtained with QTFC and PPC
procedures for differentiating patient subgroups at intake and for use in
predicting rehabilitation outcomes at discharge and work status at 1 year
after discharge from rehabilitation. Subjects. Patients (n

⫽171, 54% male;

mean age

⫽37 years, SD⫽10, range⫽18–62) with acute work-related low

back pain referred for physical therapy were analyzed. Methods. Patients
completed pain and psychosocial questionnaires at initial examination
and discharge and pain diagrams throughout intervention. Physical
therapists classified patients using QTFC and PPC data at intake. Patients
were classified again at discharge by PPC (time-dependent PPC). Results.
Analysis of variance of showed QTFC and PPC data could be used to
differentiate patients by pain intensity or disability at intake. Analysis of
covariance showed that intake PPC predicted pain intensity and disability
at discharge, but QTFC did not. Logistic regression showed that PPC
predicted work status at 1 year, but QTFC did not. Classifying patients over
time using time-dependent PPC data reduced the false positive rate by
31% and increased percentage of change in pretest-posttest probability of
return to work by 16% compared with classifying patients at intake.
Discussion and Conclusion. Results support the discriminant validity of the
QTFC data at intake and predictive validity of the PPC data at intake.
Tracking PPC over time increases predictive validity for 1-year work status.
[Werneke MW, Hart DL. Categorizing patients with occupational low
back pain by use of the Quebec Task Force Classification system versus
pain pattern classification procedures: discriminant and predictive valid-
ity. Phys Ther. 2004;84:243–254.]

Key Words: Centralization, Classification, Discriminant and predictive validity, Low back pain, Pain

pattern, Quebec Task Force.

Mark W Werneke, Dennis L Hart

Physical Therapy . Volume 84 . Number 3 . March 2004

243

Research

Report

䢇

ўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўў

ўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўў

ўўўўўўўўў

C

lassifying patients with nonspecific low back
pain into meaningful subgroups is thought to
provide assistance for clinical management

1– 4

and to increase the power of outcomes assess-

ments

1,3,5,6

and has been targeted as an important

research priority.

7,8

Use of homogeneous subgroups of

people with low back pain is considered by many experts
to be essential for the improvement of clinical trials
related to patient management and clinical outcomes.

9,10

Several classification systems have been designed to
categorize patients with low back pain into homoge-
neous subgroups that could guide clinical management
decisions or predict pain and disability.

4,6,8 –11

Of these

classification systems, the Quebec Task Force Classifica-
tion (QTFC) system

11

has received the widest review.

12–14

Health care professionals using the QTFC procedure
classify patients into 1 of 11 diagnostic categories accord-
ing to presence of pain, anatomical location of pain,
presence of neurologic signs, findings from radiological
imaging techniques, and surgical history.

11

Categories

are further subdivided according to pain duration and
patient working status. Simpler versions of the QTFC
system have been recommended for use by primary care
practitioners,

12,14

emphasizing anatomical location of

pain and results from clinical neurological assessments.

Although the QTFC system is commonly used to classify
patients, the predictive validity of data obtained with it is
debated. Atlas et al

13

reported that changes in pain and

perceived disability were associated with QTFC category
for patients following nonsurgical management. Pa-
tients with spinal nerve root compression with pain
below the knee and positive neurologic signs (QTFC
category 4) and confirmed by imaging techniques
(QTFC category 6) showed more improvement at the
1-year follow-up evaluation compared with similar
patients with pain above the knee or pain below the knee
but negative neurologic signs (QTFC categories 2 and
3). In contrast, Loisel et al

12

reported that patients with

pain below the knee with or without neurologic signs
(QTFC categories 3 and 4) were more likely to have
poorer pain and return-to-work outcomes at 1 year
compared with patients with pain but without radiation
(QTFC category 1). O’Hearn

14

reported that all patients

regardless of classification category (QTFC categories

1– 4 and 6), using a modified QTFC scheme, reported
improvements in perceived disability from initial physi-
cal therapist evaluation to discharge.

Investigators examining the prognostic validity of data
obtained with the QTFC system for future work-related
back troubles based their work on predictive models
utilizing medical information,

12–14

physical examina-

tion,

12–14

and diagnostic imaging studies.

13,14

Using this

approach, the QTFC system has been identified as a
potential predictive factor. However, we believe confi-
dence in prior results

12,13

supporting the predictive value

of the QTFC system is diminished because of the failure
to analyze psychosocial and other physical examination
factors.

Psychosocial factors are important predictors in patients
with acute low back pain at risk for future work-related
disability.

15–26

Fritz and George,

26

for example, reported

that fear-avoidance beliefs were associated with work
status after 1 month from physical therapy intervention.
Biopsychosocial multivariate models are recommended
to enhance prediction of occupational low back disabil-
ity.

16,20,22–25

Data from one recent study

27

supported the

QTFC procedure for differentiating patient categories
on the basis of intake psychological distress measures.
Frank et al

27

reported that patients with pain below the

knee were more disabled and depressed than patients
without pain radiation into the leg. However, we found
no biopsychosocial multivariate studies that investigated
the predictive validity of data obtained using the QTFC
system.

The centralization phenomenon has been reported to
be a key physical examination finding in the classifica-
tion

5,6,28

and evaluation and management of patients

with spinal impairments.

10,29 –34

McKenzie originally

defined centralization as “a situation in which pain
arising from the spine and felt laterally from the midline
or distally is reduced and transferred to a more central
or near midline position when certain movements are
performed.”

10(p22)

The reliability for the clinical docu-

mentation of centralization has been shown to be high,
with kappa values ranging from .7 to .8.

34,35

Data from

classifying patients into centralization or noncentraliza-
tion categories have been shown to be valid for predict-

MW Werneke, PT, MS, Dip MDT, is Physical Therapist, Rehabilitation Department, Spine Center, CentraState Medical Center, 901 W Main St,
Freehold, NJ 07728 (USA) ([e-mail]). Address all correspondence to Mr Werneke.

DL Hart, PT, PhD, is Director of Consulting and Research, Focus On Therapeutic Outcomes Inc, White Stone, Va.

Both authors provided concept/idea/research design and writing. Mr Werneke provided data collection, project management, subjects,
facilities/equipment, institutional liaisons, and clerical support. Dr Hart provided data analysis and consultation (including review of manuscript
before submission).

This article was received May 15, 2003, and was accepted October 17, 2003.

244 . Werneke and Hart

Physical Therapy . Volume 84 . Number 3 . March 2004

ing short- and long-term outcomes following rehabilita-
tion.

28 –32,36,37

Patients with centralizing symptoms report

better outcomes compared with similar patients without
centralizing symptoms. Yet, despite evidence that cen-
tralization can be a reliably identified physical examina-
tion finding, centralization has not been extensively
investigated using biopsychosocial predictive models
identifying patients with acute work-related low back
pain who are at risk for developing chronic disability.

We found only 2 studies in which the prognostic validity
of centralizing symptoms was compared with that of
psychosocial variables.

6,36

Karas et al

36

reported that a

high Waddell score was more predictive of return to
work regardless of the patient’s ability to report central-
ization of symptoms. In contrast, Werneke and Hart

6

reported that a pain pattern classification (PPC) system,
including centralization and noncentralization, pre-
dicted work status, as determined by telephone interview
with the patient 1 year after discharge from physical
therapy services, compared with Waddell signs and other
psychosocial factors, including fear-avoidance beliefs,
depression and somatization symptoms, and high per-
ceived pain and disability ratings.

The PPC system is a method of categorizing patients with
low back pain according to the pain they report in
response to repeated trunk movements during an initial
evaluation

28,31,32

or after multiple treatment visits.

5,6,28

We defined classification using initial evaluation data as
a “one-point-in-time classification.” Classifying patients
according to specific anatomical changes in pain loca-
tion over multiple visits we defined as a “time-dependent
classification.” One-point-in-time classification is com-
mon,

4,9,10,12–14,32

but use of time-dependent data has

been recommended as a means of improving our under-
standing of the long-term prognosis of low back
pain.

38,39

For example, Hunt et al

38

and van der Weide

et al

39

purported that there may be evolving stages of

recovery from low back pain and speculated that medical
factors may be more predictive than psychosocial factors
immediately after the onset of acute back pain. If the
patient’s pain is protracted, however, psychosocial fac-
tors may play a prominent predictive role as medical
factors become less prognostic. This hypothesized tem-
poral relationship between physical and psychosocial
factors is consistent with Waddell’s observation that
predictive models may be enhanced by assessing a
patient’s progress over time versus patient assessment at
only one point in time (ie, initial evaluation).

40

Data

collected using the time-dependent PPC procedure over
the episode of therapy were more precise than data
collected at the time of intake using one-point-in-time
PPC for discriminating pain and disability outcomes
following physical therapy intervention.

28

Because of the importance of psychosocial issues for
predicting recovery following an episode of low back
pain, the importance of classifying patients into mean-
ingful subgroups for predicting outcomes, and interest
in the validity of classifications of patients obtained using
intake or time-dependent data, we conducted this study
to assess the validity of the modified QTFC and PPC
systems using intake data for the purposes of:
(1) classifying patients on the basis of pain and disability
at initial evaluation and (2) predicting pain and disabil-
ity at the time of discharge from rehabilitation and work
status 1 year after discharge from rehabilitation. We also
used time-dependent data from the PPC to predict work
status 1 year after discharge from rehabilitation. The
results may help clarify differences between 2 classifica-
tion procedures and differences between one-point-in-
time versus time-dependent classification techniques for
clinical practice and research.

Method

Subjects
This is a secondary analysis of a previously described
cohort of patients.

5,6

The original design was a prospec-

tive data collection of 351 consecutive patients between
the ages of 18 and 65 years referred for physical therapy
with recent onset of nonspecific neck or low back pain
and having symptoms of less than 6 weeks’ duration.
Patients were excluded if they refused to sign a consent
form, reported spinal pain or work loss within 6 months
before this episode, were unable to complete intake
questionnaires, or had poor English proficiency, prior
spinal surgery, pregnancy, spinal stenosis, or serious
spinal pathology. Fifty-one patients did not meet the
admission criteria. For this study, we selected patients
(n

⫽171) who were receiving workers’ compensation

benefits following a work-related low back pain incident
with complete data sets for independent and dependent
variables (Tab. 1).

25,26,41– 48

Patients were referred by

their physicians to 1 of 2 physical therapy outpatient
clinics within the same municipality. Five physical ther-
apists participated in the study, and all therapists
received advanced training in McKenzie evaluation and
treatment methods.

The characteristics of the patients are shown in Table 1.
At the time of intake (one-point-in-time), 123 patients
(72%) reported low back pain without radiation below
the gluteal fold (QTFC category 1), 25 patients (14%)
reported back pain radiating to above the knee (QTFC
category 2), 20 patients (12%) reported pain radiating
below the knee (QTFC category 3), and 3 patients (2%)
reported distal pain and had at least 2 positive neuro-
logical signs. We merged QTFC categories 1 and 2 and
QTFC categories 3 and 4 for validity calculations. Intake
PPC consisted of 2 classification categories: 77 patients

Physical Therapy . Volume 84 . Number 3 . March 2004

Werneke and Hart . 245

ўўўўўўўўўўўўўўўўўўўўўўўўўўўў

(45%) were classified into the centralization category,
and 94 patients (55%) were classified into the noncen-
tralization category. Time-dependent PPC at the time of
discharge from rehabilitation consisted of 3 classifica-
tion categories: 49 patients (29%) were classified into
the centralization category, 78 patients (46%) were
classified into the partial reduction category, and 43
patients (25%) were classified into the noncentralization

category. One patient did not have discharge data for
time-dependent PPC identification. For predictive valid-
ity of time-dependent data at 1 year, centralization and
partial reduction categories were merged because previ-
ous research demonstrated no difference in outcomes
between these 2 groups.

6

Procedure
The procedures used in this study have been described
previously.

5,6

Briefly, before initial physical therapist

examination, patients completed a battery of question-
naires designed to gather information related to medi-
cal, demographic, pain, job, and psychosocial factors. In
addition, at intake and at discharge, patients completed
a pain intensity scale

49

and the Oswestry Low Back Pain

Disability Questionnaire.

41

Body diagrams were com-

pleted before and after each visit, including the initial
examination, to determine anatomical pain response
from mechanical examination.

5

After the patients completed intake questionnaires, a
mechanical evaluation following McKenzie’s assessment
methods was done by one of the 5 physical therapists
who were credentialed (n

⫽2) or diplomats (n⫽3) in

McKenzie methods.

5

Interrater reliability of low back

pain assessments by therapists with advanced creden-
tialing in the McKenzie system has been previously
reported.

33,35

For example, Kilpikoski et al

35

reported

satisfactory agreement on the relevance of lateral shift
(

␬⫽.7), repeated movement tests to define centraliza-

tion (

␬⫽.7) and directional preference of exercise

(

␬⫽.9), and classification into specific McKenzie sub-

groups (

␬⫽.7). In addition, the following physical exam-

ination tests were completed for patients reporting leg
pain radiating below the knee: straight leg raise (SLR),
knee/ankle/foot manual muscle tests (MMT), light
touch for sensation tests, and ankle and knee deep
tendon reflex tests. An SLR was considered positive if the
patient’s familiar calf/foot symptoms were below 60
degrees of leg elevation as measured with a gonio-
meter.

50

Manual muscle testing

51

of knee extension

(L3), ankle dorsiflexion (L4), large toe extension (L5),
and ankle plantar flexion (S1) was done, although the
reliability of these measurements is questionable. An
MMT grade was considered positive if the muscle’s score
was graded as reduced compared with the uninvolved
side according to the therapist’s judgment. Light touch
sensation testing was performed for the L3 to S1 der-
matomes.

52

A sensory test was considered positive if light

touch was graded as reduced compared with the unin-
volved side according to the therapist’s judgment. Knee
and ankle reflexes were tested using a standard reflex
hammer and were judged as positive tests if graded as
absent or reduced compared with the uninvolved side.

Table 1.

Patient Characteristics (n

⫽171)

Characteristic

Value

At the time of intake

Sex

Male

54%

Female

46%

Age (y)

X

37

SD

10

Range

18–62

Days off work

X

4

SD

7

Range

0–28

Days between incident and initial evaluation

X

12

SD

9

Range

1–42

Multiple sites of pain

19%

Initial pain below knee

13%

Initial pain intensity of

ⱖ6 out of 10

81%

History of prior spinal pain

43%

History of prior days lost from work

12%

History of prior worker-related complaint

12%

Not working full-time at full duty

96%

Low work satisfaction

43,a

46%

High nonorganic physical signs

44,b

11%

High fear-avoidance of physical activities

45,a

49%

High fear-avoidance of work activities

26,45,c

30%

High depressive symptoms

46,a

46%

High somatization of symptoms

46,a

47%

High disability rating

25,41,42,d

64%

Straight leg raise positive at

ⱕ60°

4%

Overt pain behavior

47,48,e

15%

Quebec Task Force Classification pain below the

knee

13%

Noncentralizing symptoms

55%

At the time of discharge from rehabilitation

Noncentralizing symptoms

25%

a

High/low score determined by median split.

b

At least 3 of 5 nonorganic physical signs.

44

c

High score of 35 or more on a scale of 0 to 42.

26

d

High score of 40 or more on a scale of 0 to 100.

25,41,42

e

High score of 2 or more for overt pain behaviors.

47,48

246 . Werneke and Hart

Physical Therapy . Volume 84 . Number 3 . March 2004

Patients were classified at 2 different times: at the time of
intake and at the time of discharge. At the time of intake,
evaluating physical therapists classified patients (first
classification process) by determining if patient symp-
toms were centralized (centralization category) or were
not

centralized

(noncentralization

category),

and

patients were classified (second classification process)
using the QTFC categories. There were no patients in
QTFC categories 5 through 11

11

because the inclusion

criteria excluded these patients. The remaining 4 cate-
gories represent a method of classification based on pain
location and clinical examination of neurological signs
(ie, motor, sensory, and reflex). For our study, we
followed a truncation recommended by Loisel et al

12

for

QTFC categories. Loisel et al recommended using the
first 4 QTFC categories for patients without surgery who
were evaluated during the early stage of nonserious back
pain. The QTFC categories 5 to 11 were excluded
because of the study’s inclusion criteria. The QTFC
categories 1 and 2 were combined and QTFC categories
3 and 4 were combined, producing a dichotomous
classification system based on whether or not pain
radiated below the knee. Patients were classified (third
classification process) at the time of discharge from
rehabilitation into groups on the basis of having one of
3 anatomical pain patterns (centralization, noncentral-
ization, and partial reduction) after multiple treatment
visits,

5

which we defined as time-dependent PPC.

The evaluating physical therapist treated each patient. If
the evaluating therapist’s schedule was changed unex-
pectedly, another physical therapist participating in the
study may have treated the patient. Exercises, manual
techniques, and cognitive-behavioral educational strate-
gies

53

were provided as deemed necessary by the treating

physical therapist and are described elsewhere.

5

Our

study was designed to assess discriminant and predictive
validity of data obtained with the 2 classification proce-
dures and, therefore, there was no attempt to standard-
ize or influence care across patient classification
procedures.

Outcome Measures
Pain intensity and perceived disability were assessed at
the time of intake and at the time of discharge from
rehabilitation. Maximal pain intensity experienced dur-
ing the preceding 24 hours was assessed using an
11-point numeric pain scale: 0 (no pain) to 10 (severe
emergency-department-type pain).

49,54

The 11-point

pain scale has been shown to yield reliable and valid
measurements of pain intensity.

49,54

Low back-related

disability was assessed using the 10-item Oswestry Low
Back Pain Disability Questionnaire.

41

The disability score

is expressed as a percentage, with higher scores repre-
senting more disability. Data from the Oswestry ques-
tionnaire have been shown to have good test-retest

reliability

41

and predictive validity.

25,42

In the original

study,

41

22 patients with chronic low back pain com-

pleted the Oswestry questionnaire on 2 consecutive days,
producing a correlation coefficient of .99. Cooper et al

55

measured change in Oswestry questionnaire scores
between the time of injury and a 6-month follow-up
evaluation and reported that high disability at the time
of injury was associated with high disability at the
6-month follow-up evaluation (P

⬍.01). Tate et al

42

reported that perceived disability as measured with the
Oswestry questionnaire predicted (P

⬍.001) duration of

time loss due to back symptoms and predicted future lost
work time. Nordin et al

25

reported that Oswestry scores

greater than 40 out of 100 predicted delayed return to
work in patients with serious functional disability (odds
ratio

⫽1.40, 95% confidence interval [CI]⫽1.05–1.88,

P

⬍.02).

Work status was assessed 1 year after discharge from
rehabilitation. Work status was considered good if the
employee was working full-time at full duty. A poor
outcome was defined as when a previously full-time
employee was currently working less than full-time at full
duty because of the low back pain problems for which
the patient was managed. An occupational nurse who
was experienced in conducting structured telephone
interviews and who was masked (blinded) to classifica-
tion categories and response to intervention called all
patients to assess work status at 1 year after discharge
from rehabilitation.

Data Analysis
To accomplish the 3 study purposes, several sets of
analyses were conducted. For purpose 1, validity of
QTFC and PPC was assessed using intake data to differ-
entiate

patients

by

pain

intensity

(0 –5

⫽low,

6 –10

⫽high)

56

and disability (Oswestry questionnaire

scores of 0 –39

⫽low and 40–100⫽high)

25,41,42

at initial

evaluation by calculating one-way analyses of variance
(ANOVAs). We assessed discriminant validity at the time
of intake by determining differences for the dependent
variables pain intensity and perceived disability across
PPC and QTFC categories. Power (power

⫽1⫺

␤) analy-

ses were performed on all ANOVA results if the results of
one ANOVA were not significant.

57

For all analyses,

␣⫽.05.

Our ability to use intake classification data to predict
which patients would have high pain or disability at the
time of discharge from rehabilitation was assessed by
determining differences in dependent variables across
categories of classification procedures using one-way
analyses of covariance (ANCOVAs). Pain intensity at the
time of discharge was compared across QTFC and PPC
categories using intake pain intensity as the covariate.
Perceived disability was compared across classification

Physical Therapy . Volume 84 . Number 3 . March 2004

Werneke and Hart . 247

ўўўўўўўўўўўўўўўўўўўўўўўўўўўў

categories using intake perceived disability as the covari-
ate. Power (power

⫽1⫺

␤) analyses were performed on

all ANCOVA results if the results of one ANCOVA were
not significant.

57

For purpose 2, our ability to use intake data to predict
which patients would have less than optimal work status
1 year after discharge from rehabilitation was deter-
mined using 3 sets of analyses. First, the relationship of
each of the 22 independent variables at the time of
intake (Tab. 1) to work status was assessed with univari-
ate analyses. Two-sample t tests were used to compare
continuous independent variables and work status, and
chi-square tests of independence were used to compare
categorical independent variables and work status.

Second, independent variables (Tab. 1) related to poor
work status assessed by the univariate analyses were
entered into a complete multivariate logistic regression
model to assess work status.

58,59

We used the Hosmer-

Lemeshow summary goodness-of-fit statistic to assess fit
of the model to the data. Higher probability values
indicate better fit.

59

Likelihood ratio (LR) chi-square

and McFadden rho statistics were calculated for the
logistic model. A t-ratio (regression coefficient divided
by associated standard error) and odds ratio with 95%
CIs were calculated for each independent variable in
each final logistic model.

59

Third, we examined independent variables from the
logistic regression analyses for their ability to predict
work status by calculating sensitivity, specificity, positive
and negative likelihood ratios (

⫹LR, ⫺LR), and positive

and negative predictive values (PPV, NPV).

60

To calcu-

late sensitivity and specificity, a 2

⫻2 contingency table

was used. Patients who were unable to return to work
full-time at full duty formed the disease-positive group of
the target disorder. Patients returning to full-time, full-
duty work formed the disease-negative group of the
target disorder. Patients with pain below the knee
(QTFC category 3 or 4) or whose symptoms were not
centralized (PPC noncentralization) formed the diag-
nostic test-positive group. Patients with pain above the
knee (QTFC category 1 or 2) or whose symptoms were
centralized (PPC centralization) formed the diagnostic
test-negative group. Sensitivity is the proportion of
patients with the target disorder (ie, less than optimal
work status) who have positive test results (ie, pain below
the knee or noncentralized).

60,61

Specificity is the propor-

tion of patients who do not have the target disorder (ie,
return to work without restrictions) and who have a
negative test result (ie, no pain below the knee or
centralized).

60,61

Positive likelihood ratios were calculated as sensitivity/
1

⫺specificity, and ⫺LRs were calculated as 1⫺sensitivity/

specificity.

60

As described elsewhere,

62

LRs are summary

measures of diagnostic test performance (ie, classifica-
tion) that indicate how much a given classification will
raise or lower the pretest probability of the target
disorder of interest (ie, work status).

60,61,63

Following a

published guide,

64

acceptable

⫹LRs are 2 or more and

acceptable

⫺LRs are 0.5 or less because they generate at

least small, but possibly important, changes in predictive
value of the test. Positive predictive value is defined as the
probability of having the target disorder when the test
result is positive.

60,61

Negative predictive value is defined as

the probability of absence of the target disorder if the
test result is negative.

61

The PPV and NPV are affected by

sensitivity, specificity, and classification prevalence. Prev-
alence, which is equal to pretest probability, was calcu-
lated as the number of patients with the target disorder
divided by all patients tested.

60

The higher the

⫹LR, the

more predictive a positive test will be for a given preva-
lence. Absolute values of

⫺LR will increase with dimin-

ishing discriminative power of patient classification,

61

so

the smaller the

⫺LR value, the higher the negative

predictive value for a given prevalence.

61

The 95% CIs

were calculated for sensitivity, specificity,

⫹LR, ⫺LR,

PPV, and NPV.

65

The diagnostic accuracy of independent variables from
the final logistic regression analysis was considered
acceptable if: (1) either

⫹LR was 2 or more or ⫺LR was

0.5 or less

64

and (2) the posttest probability was 15% or

more. On the basis of pretest probability for a poor
return-to-work outcome of 15% in this cohort of
patients,

⫹LR values of 2 or more and ⫺LR values of

⬍0.5 would result in a posttest probability change of
approximately 10%.

66

For purpose 3, ability of time-dependent PPC data to
predict work status 1 year after discharge from rehabili-
tation was assessed using the same sets of analyses
described above for purpose 2 except for one change:
one-point-in-time PPC was supplanted with time-
dependent PPC assessed at the time of discharge from
rehabilitation (Tab. 1).

Results

Discriminant Validity of Intake Patient Classification
For one-point-in-time analyses at the time of intake,
QTFC was used to differentiate patients on the basis of
pain intensity and disability, and PPC was used to
differentiate patients on the basis of disability (Tab. 2).
Only PPC classification procedure predicted pain inten-
sity and disability at the time of discharge from rehabil-
itation (Tab. 3).

248 . Werneke and Hart

Physical Therapy . Volume 84 . Number 3 . March 2004

Contacted Patients Versus Noncontacted Patients
Analyses
Of the 171 patients selected, 136 patients (80%) were
contacted by telephone, 4 patients refused to be inter-
viewed, and 132 patients were successfully interviewed
(77% follow-up rate). Of all of the independent variables
(Tab. 1), only one variable was different between groups:
contacted patients were older than noncontacted
patients (mean years of age

⫽39 [SD⫽10] versus mean

years of age

⫽33 [SD⫽9], t⫽3.8, df⫽78.1, P⫽.001).

Predictive Validity of One-Point-in-Time Data at 1 Year
After Discharge From Rehabilitation
The results of the univariate analyses are displayed in
Tables 4 and 5.

25,26,41– 48

Four independent variables

affected work status: multiple sites of pain, high pain
intensity, high fear-avoidance of work activities, and
noncentralizing symptoms. The QTFC categories were
not related to work status. Results of the logistic regres-

sion analyses demonstrated that overall fit of the model
was supported (Hosmer-Lemeshow goodness-of-fit statis-
tic

59

for complete model

⫽.17, df⫽2, P⫽.92; McFadden

rho

67

⫽.12). In the final model, only intake PPC pre-

dicted work status at 1 year after discharge from reha-
bilitation (standardized t-ratio coefficient

⫽2.8, P⫽.005;

maximum

likelihood-ratio

statistic

⫽12.2,

df

⫽1,

P

⬍.001).

59

Patients classified as having noncentralized

symptoms were almost 9 times more likely not to return
to work (odds ratio

⫽8.8, 95% CI⫽1.9–40.1). Findings

for accuracy of PPC for predicting work status statistics
were as follows: sensitivity

⫽0.89 (95% CI⫽0.69–0.97),

specificity

⫽0.51 (95% CI⫽0.42–0.60), ⫹LR⫽1.82 (95%

CI

⫽1.42–2.34), ⫺LR⫽0.21 (95% CI⫽0.06–0.28),

PPV

⫽0.25 (95% CI⫽0.16–0.36), and NPV⫽0.96 (95%

CI

⫽0.88–0.99). A patient demonstrating a lack of cen-

tralization during initial evaluation (15% prevalence)
produced a pretest-posttest probability change of 9%.

Table 2.

Classification Systems for Differentiating Patients on the Basis of Pain and Disability at the Time of Initial Evaluation

Classification Procedure

a

Category

Mean

b

(SE)

F

c

P

c

Power

c

Pain at time of intake

PPC

Centralization (n

⫽77)

7.5 (0.3)

3.2

.08

.40

Noncentralization (n

⫽94)

8.1 (0.2)

QTFC

Pain above knee (n

⫽148)

7.7 (0.2)

7.9

.005

.55

Pain below knee (n

⫽23)

9.0 (0.5)

Disability at time of intake

d

PPC

Centralization (n

⫽77)

41.0 (1.6)

8.3

.004

.78

Noncentralization (n

⫽94)

47.3 (1.5)

QTFC

Pain above knee (n

⫽148)

43.1 (1.2)

9.7

.002

.64

Pain below knee (n

⫽23)

53.1 (3.0)

a

PPC

⫽pain pattern classification, QTFC⫽Quebec Task Force Classification (modified).

b

Adjusted least square mean (standard error).

c

F, P, and power (1

⫺

␤) for main factor (classification procedure) for analyses of variance.

d

Oswestry Low Back Pain Disability Questionnaire scores.

Table 3.

Classification Systems for Predicting Pain Intensity and Disability at Time of Discharge From Rehabilitation

Classification Procedure

a

Category

Mean

b

(SE)

F

c

P

c

Power

c

Pain at time of discharge

PPC

Centralization (n

⫽76)

1.6 (0.3)

28.9

⬍.001

.82

Noncentralization (n

⫽94)

3.9 (0.3)

QTFC

Pain above knee (n

⫽147)

2.8 (0.2)

2.3

.14

.22

Pain below knee (n

⫽23)

3.8 (0.6)

Disability at time of discharge

d

PPC

Centralization (n

⫽76)

13.6 (1.8)

25.3

⬍.001

1.0

Noncentralization (n

⫽94)

25.6 (1.6)

QTFC

Pain above knee (n

⫽147)

19.5 (1.3)

2.2

.14

.25

Pain below knee (n

⫽23)

25.1 (3.4)

a

PPC

⫽pain pattern classification, QTFC⫽Quebec Task Force Classification (modified).

b

Adjusted least square mean (standard error).

c

F, P, and power (1

⫺

␤) for main factor (classification procedure) for analyses of variance.

d

Oswestry Low Back Pain Disability Questionnaire scores.

Physical Therapy . Volume 84 . Number 3 . March 2004

Werneke and Hart . 249

ўўўўўўўўўўўўўўўўўўўўўўўўўўўў

Predictive Validity of Time-Dependent Data at 1 Year
After Discharge From Rehabilitation
In addition to univariate analyses of intake data (Tabs. 4
and 5), time-dependent PPC results are displayed in
Table 5. Time-dependent PPC assessed at discharge was
added to multiple sites of pain, high pain intensity, and
high fear-avoidance of work activities assessed at the time
of intake for the logistic regression analysis.

59,67

Overall

fit of the model was supported (Hosmer-Lemeshow
goodness-of-fit statistic

59

⫽2.5, df⫽3, P⫽.48, McFadden

rho

67

⫽.18). In the final model, only time-dependent

PPC predicted work status at 1 year after discharge from
rehabilitation

(standardized

t-ratio

coefficient

⫽4.1,

P

⬍.001; maximum likelihood-ratio statistic⫽18.8, df⫽1,

P

⬍.001).

59

Patients classified as having noncentraliza-

tion of pain were almost 10 times more likely not to
return to work (odds ratio

⫽9.9, 95% CI⫽3.3–29). Find-

ings for accuracy of PPC for predicting work status
statistics were as follows: sensitivity

⫽0.68 (95% CI⫽0.46–

0.85), specificity

⫽0.82 (95% CI⫽0.74–0.88), ⫹LR⫽3.82

(95% CI

⫽2.29–6.35), ⫺LR⫽0.38 (95% CI⫽0.20–0.75),

PPV

⫽0.41 (95% CI⫽0.26–0.58), and NPV⫽0.94 (95%

CI

⫽0.87–0.97). A patient demonstrating no centraliza-

tion of symptoms at the time of discharge (15% preva-
lence) produced a pretest-posttest probability change
of 25%.

Discussion
Classifying patients with acute, occupational, and non-
specific low back pain syndromes by pain above or below
the knee (QTFC categories 1– 4)

12

can be used to

identify patients who have high or low pain intensity or
perceived disability at the time of initial evaluation.
Intake QTFC categories as grouped in this study were
not predictive of pain intensity or disability at the time of
discharge from rehabilitation or of work status 1 year
after discharge from rehabilitation. Intake pain pattern
classification

28

differentiated patients by perceived dis-

ability, but the primary value of one-point-in-time PPC
was in predicting pain and disability at the time of
discharge and work status 1 year after discharge from
rehabilitation. The predictive value of PPC increased
when classification was followed over the rehabilitation
episode. Our data supported the idea that not only is

anatomical location of pain important for differentiating
patients on the basis of disability at the time of intake,
but a change in anatomical location of pain following
clinician-directed examination procedures was predic-
tive of future pain intensity, disability, and work status in
this sample. The results of our study contribute to the
existing literature by: (1) clarifying differences between
2 classification systems, (2) supporting literature recom-
mending assessment of change in anatomical location of
pain during patient examination, and (3) supporting
time-dependent data

38 – 40

and patient classification pro-

cedures

6,28

as stronger predictors of work status than the

same data or classification assessed at one point in time.

Using the presence of pain above or below the knee at
the time of initial evaluation for differentiating patients
on the basis of baseline disability is consistent with the
findings of previous studies.

12,13,27

Our results do not

support the use of location of leg pain for predicting
pain intensity and disability at the time of discharge from
rehabilitation. This finding is similar to the findings of
O’Hearn,

14

who reported decreases in perceived disabil-

ity at the time of discharge from rehabilitation for all
patients with acute or subacute symptoms regardless of
baseline modified QTFC categories 1 through 4 and 6.

Pain below the knee has been reported to be an impor-
tant predictor of poor outcomes in people with low back
pain.

12,18,39

Loisel et al,

12

for example, reported that

patients with pain below the knee during initial evalua-
tion (QTFC categories 3 and 4) were less likely to return
to regular work compared with patients with back pain
without radiation (QTFC category 1). In contrast, pain
below the knee with or without positive neurological
signs (QTFC categories 3 and 4) was not predictive of
work loss at 1 year after discharge from rehabilitation in
our study. There are 2 reasons that might explain the
poor predictive validity for leg pain. First, back and leg
pain were grouped using a dichotomous classification,
which might have decreased precision secondary to lost
information. Patients in our study, however, were
referred for physical therapy early with acute low back
pain, so QTFC categories 5 through 11 would not be
expected for this sample unless radiological imaging was

Table 4.

Univariate Tests for Continuous Intake Variables, With Work Status at 1 Year After Discharge From Rehabilitation as Dependent Variable

Variable

Persistent Restrictions (n

ⴝ19)

No Restrictions (n

ⴝ106)

Mean Difference
(95% CI

a

)

P

X

SD

Range

X

SD

Range

Age (y)

40

11

24–60

39

10

18–62

⫺1.2 (⫺6.7–4.3)

1.00

Days off work

6

7

0–21

4

7

0–28

⫺2.4 (⫺6.1–1.3)

.98

Acuity

b

14

12

1–42

12

9

1–42

⫺2.2 (⫺8.2–3.7)

1.00

a

CI

⫽confidence interval.

b

Acuity

⫽days between date of first symptoms and date of initial evaluation.

250 . Werneke and Hart

Physical Therapy . Volume 84 . Number 3 . March 2004

required to rule out serious pathology. In addition, few
patients in our sample reported pain below the knee
with neurological signs, which supports findings from
other studies.

12,14,27

Second, in only one prior study

6

were one-point-in-time PPC and leg pain as independent
variables used in a predictive biopsychosocial multivari-
ate model. In that study, lack of centralization during
clinical evaluation improved the likelihood of poor
outcomes following conservative intervention regardless

of distal leg pain location. Anatomical
location of pain at the time of initial
evaluation (QTFC categories 1– 4) lost
predictive power when entered into
multivariate biopsychosocial predictive
models, but change in anatomical loca-
tion of pain in response to standardized
repeated lumbar movement tests did
not.

6

Our results allow comparison of the
predictive accuracy of the PPC system
determined at one point in time versus
classifying patients over the rehabili-
tation episode (ie, time-dependent
classification). In our sample, one-point-
in-time PPC had relatively high sensitiv-
ity (95% CI

⫽0.69–0.97), acceptable

⫺LR (95% CI⫽0.06–0.28), and high
NPV (95% CI

⫽0.88–0.99). One-point-

in-time PPC produced a modest 9%
change in pretest-posttest probability of
return to work given a low (15%) prev-
alence of patients not working at 1 year
after discharge from rehabilitation.
The

result

of

any

clinical

test

(eg, repeated trunk movements) can
be interpreted as an argument to
strengthen or weaken conviction of
prediction

of

the

target

disorder

(eg, return-to-work status) based on the
available information on the patient.

61

In our study, PPC had good sensitivity,
so if the clinician finds that his or her
patient’s symptoms are centralized,
poor work status could be effectively
ruled out.

60

One purpose of the PPC procedure is
to identify patients at risk for poor work
status at 1 year after physical therapy
intervention. Targeting patients who
might have difficulty returning to work
for costly comprehensive multidisci-
plinary interventions designed to pre-
vent future disability during the acute
phase of pain could be advantageous
while avoiding unnecessary and costly

interventions for patients who are likely to return to
work easily. Subsequently, reducing false positive results
is beneficial. The false positive rate (ie, probability of
noncentralization given a patient who returns to work)
for one-point-in-time PPC was 49%.

61

The

⫺LR, which in

our study was good, expresses how many times less likely
a normal test result (ie, symptoms centralized) is to be
expected in patients who do not return to work as

Table 5.

Univariate Tests for Categorical Variables, With Work Status at 1 Year After Discharge
From Rehabilitation as Dependent Variable

Variable

Persistent
Restrictions
(n

ⴝ19)

No
Restrictions
(n

ⴝ106)

␹

2a

df

a

P

a

At time of intake

Sex (male)

11

47

1.2

1

.28

Multiple sites of pain

7

18

4.0

1

.05

Initial pain below knee

4

15

0.6

1

.44

Initial pain intensity

ⱖ6 out of

10

19

83

5.1

1

.03

History of prior spinal pain

6

48

1.2

1

.27

History of prior days lost from

work

2

13

0.1

1

.83

History of prior worker-related

complaint

2

14

0.1

1

.75

Not working full-time at full duty

at time of intake

17

103

2.5

1

.12

Low work satisfaction

43,b

8

45

⬍0.1 1

.98

High nonorganic physical

signs

44,c

3

10

0.7

1

.40

High fear-avoidance of physical

activities

45,b

7

52

1.0

1

.33

High fear-avoidance of work

activities

26,45,d

9

26

4.2

1

.04

High depressive symptoms

46,b

7

46

0.3

1

.59

High somatization of

symptoms

46,b

11

45

1.6

1

.21

High disability rating

25,41,42,e

15

64

2.4

1

.12

Straight leg raise positive at

ⱕ60°

1

6

⬍0.1 1

.95

Overt pain behavior

47,48,f

5

11

3.7

1

.06

Quebec Task Force

Classification pain below
knee

4

15

0.6

1

.44

Noncentralizing symptoms

17

52

10.6

1

⬍.01

At time of discharge

Noncentralizing symptoms

13

19

21.6

1

⬍.01

a

P values and degrees of freedom are for chi-square statistics.

b

High/low score determined by median split.

c

At least 3 of 5 nonorganic physical signs.

44

d

High score of 35 or more on a scale of 0 to 42.

26

e

High score of 40 or more on a scale of 0 to 100.

25,41,42

f

High score of 2 or more for overt pain behaviors.

47,48

Physical Therapy . Volume 84 . Number 3 . March 2004

Werneke and Hart . 251

ўўўўўўўўўўўўўўўўўўўўўўўўўўўў

compared with patients who return to work.

61

The

smaller the

⫺LR, the higher the negative predictive

value of PPC for a given prevalence.

61

Thus, although

sensitivity,

⫺LR, and NPV were adequate, the false

positive rate was not. A high false positive rate may cause
unnecessary testing or intervention.

61

Time-dependent PPC had relatively high specificity
(95% CI

⫽0.74–0.88), modest sensitivity (95% CI⫽0.46–

0.85), acceptable

⫹LR (95% CI⫽2.29–6.35), acceptable

⫺LR (95% CI⫽0.20–0.75), and high NPV (95%
CI

⫽0.87–0.97). The time-dependent PPC identified a

25% change in pretest-posttest probability of return to
work given the same low (15%) prevalence of patients
whose symptoms were not centralized and on whom we
had return-to-work data. Results of time-dependent
patient classification following testing of repeated trunk
movements are clearly more predictive of 1-year work
status compared with one-point-in-time classification.

61

A

higher specificity and reduced false positive rate (18%)
were found. When specificity is high, a positive result
(ie, symptoms do not centralize) effectively rules in poor
work status.

60

If one considers that the

⫹LR can be

interpreted as a cost-benefit ratio with the numerator or
true positive rate (68%) representing a benefit criterion
and the denominator or false positive rate (18%) repre-
senting cost,

61

time-dependent PPC appears to be a

better clinical tool to direct intervention than one-point-
in-time PPC if work status is of interest.

In contrast to previous studies,

68 –70

our data do not

support psychosocial factors as important predictors of
future work-related disability. There is a consensus
among experts that psychosocial factors are better than
medical factors for explaining chronic low back pain and
disability.

16,20,22,23,71

Despite this popular belief, we

believe this is an oversimplification. Both physical and
nonbiological factors may play important predictive
roles depending on when the predictive model is
applied during the course of back pain.

38,39

Our

research suggests to us that physical factors (ie, changes
in anatomical pain location in response to repeated
trunk movement testing) are better predictors of future
disability than are psychosocial variables measured dur-
ing the acute phase of back pain. The patient’s responses
to physical clinical examination tests, however, may be
affected by psychosocial influences.

72

The ability to use

centralization for prediction as analyzed by biopsycho-
social multivariate models for subacute and chronic low
back pain and disability warrants future investigation.

Limitations
The noncontacted group in our study was younger than
the contact group. We do not believe that the age
difference between the 2 groups was a factor in our
results. Although the difference was significant, we

believe it was small enough to be considered clinically
unimportant. Both groups were in their fourth decade of
life, and the difference between groups was 6 years.
There is no consensus on the importance of age as a
predictive factor, and researchers

18 –20,73

have reported

conflicting affects of age on disability and work status.

We investigated anatomical pain patterns utilizing a
prospective cohort design. Such a design, we contend, is
optimal for examining a diagnostic test (eg, centraliza-
tion) and its relationship to the reference standard
(ie, return-to-work status). However, randomized con-
trol trials are required to elucidate whether the results of
classifying patients based on pain patterns lead to more
effective interventions. Effects of exercises such as those
proposed by McKenzie

10

have not been rigorously inves-

tigated,

74

and effects of exercises prescribed for specific

patient classifications are still under review.

1,3

Whether

general exercises can be designed to modify patients’
beliefs concerning pain and activity following an acute
episode of low back pain also warrants investigation.

Generalizability of the PPC model for patients with
chronic low back pain has not been investigated. In
addition, in our study, QTFC categories 3 and 4 were
merged because only 3 patients were classified into
QTFC category 4. The small number of patients in the
QTFC category 4 limits our results for patients with
positive neurological findings. However, the predictive
role of neurological clinical signs for identifying patients
with low back pain who are at risk for future work-related
disability can be questioned.

22,23,25,71

Future research is

needed to investigate centralization classification models
for patients with either chronic low back pain syndromes
or neurological deficits.

The predictive validity of the modified QTFC system
investigated in our study may have been affected by the
dichotomous subgroupings we analyzed (ie, QTFC cate-
gories 1 and 2 and categories 3 and 4 were combined).
However, we chose these 2 subgroups based on Loisel
and colleagues’ QTFC stratification recommendations
for patients in primary care.

12

In addition, these sub-

groups appear logical in light of previous research
suggesting that patients with sciatica (ie, pain below the
knee) are at risk for poor treatment outcomes.

18,39

Summary and Conclusion
When clinicians want to predict pain and disability at the
time of a patient’s discharge from rehabilitation or a
patient’s long-term work status, classifying the patient
according to change in anatomical location of pain over
the treatment episode is more predictive than classifying
the patient by anatomical location at one point in time
or classifying the patient with pain above or below the
knee during an acute episode of low back pain.

252 . Werneke and Hart

Physical Therapy . Volume 84 . Number 3 . March 2004

References

1

Delitto A, Cibulka M, Erhard R, et al. Evidence for use of an

extension-mobilization category in acute low-back syndrome: a pre-
scriptive validation pilot study. Phys Ther. 1993;73:216 –222.

2

Erhard RE, Delitto A, Cibulka MT. Relative effectiveness of an

extension program and a combined program of manipulation and
flexion and extension exercises in patients with acute low-back syn-
drome. Phys Ther. 1994;74:1093–1100.

3

Fritz JM, George SZ. The use of a classification approach to identify

subgroups of patients with acute low-back pain: interrater reliability
and short-term treatment outcomes. Spine. 2000;25:106 –114.

4

Wilson L, Hall H, McIntosh G, Melles T. Inter-tester reliability of a

low-back pain classification system. Spine. 1999;24:248 –254.

5

Werneke MW, Hart DL, Cook D. A descriptive study of the central-

ization phenomenon: a prospective analysis. Spine. 1999;24:676 – 683.

6

Werneke MW, Hart DL. Centralization phenomenon as a prognostic

factor for chronic low-back pain and disability. Spine. 2001;26:758 –765.

7

Borkan JM, Koes B, Reis S, Cherkin DC. A report from the Second

International Forum for Primary Care Research on Low-back Pain:
re-examining priorities. Spine. 1998;23:1992–1996.

8

Riddle DL. Classification and low-back pain: a review of the literature

and critical analysis of selected systems. Phys Ther. 1998;78:708 –737.

9

Delitto A, Erhard RE, Bowling RW. A treatment-based classification

approach to low-back syndrome: identifying and staging patients for
conservative treatment. Phys Ther. 1995;75:470 – 485.

10

McKenzie R. The Lumbar Spine: Mechanical Diagnosis and Therapy.

Waikanae, New Zealand: Spinal Publication Ltd; 1981.

11

Spitzer WO. Scientific Approach to the Assessment and Measure-

ment of Activity-Related Spinal Disorders: A Monograph for Clini-
cians—Report of the Quebec Task Force on Spinal Disorders. Spine.
1987;12(suppl):S1–S59.

12

Loisel P, Vachon B, Lemaire J, et al. Discriminative and predictive

validity assessment of the Quebec Task Force Classification. Spine.
2002;27:851– 857.

13

Atlas SJ, Deyo RA, Patrick DL, et al. The Quebec Task Force

Classification for spinal disorders and the severity, treatment, and
outcomes of sciatica and lumbar spinal stenosis. Spine. 1996;21:
2885–2892.

14

O’Hearn MA. Physical therapy treatment of low back pain: a report

of outcomes according to three types of patient classification. J Rehabil
Outcomes Meas. 1997;1:23–31.

15

Accident Rehabilitation and Compensation Insurance Corporation

and the National Health Committee. New Zealand Acute Low Back Pain
Guide. Wellington, New Zealand: Ministry of Health; 1997:1–13.

16

Burton AK, Tillotson KM, Main CJ, Hollis S. Psychosocial predictors

of outcome in acute and subchronic low-back trouble. Spine. 1995;20:
722–728.

17

Carey TS, Garrett JM, Jackman AM. Beyond a good prognosis:

examination of an inception cohort of patients with chronic low back
pain. Spine. 2000;25:115–120.

18

Cherkin DC, Deyo RA, Street JH, Barlow W. Predicting outcomes

for back pain seen in primary care using patient’s own criteria. Spine.
1996;21:2900 –2907.

19

Coste J, Delecoeuillerie G, Cohen de Lara A, et al. Clinical course

and prognostic factors in acute low-back pain: an inception cohort
study in primary care practice. BMJ. 1994;308:577–580.

20

Deyo RA, Diehl AK. Psychological predictors of disability in patients

with low-back pain. J Rheumatol. 1988;15:1557–1564.

21

Dionne CE, Koepsell TD, Von Korff M, et al. Predicting long-term

functional limitations among back pain patients in primary care
settings. J Clin Epidemiol. 1997;50:31– 43.

22

Hasenbring M, Marienfeld G, Kuhlendahl D, Soyka D. Risk factors

of chronicity in lumbar disc patients: a prospective investigation of
biologic, psychologic, and social predictors of therapy outcome. Spine.
1994;24:2759 –2765.

23

Hazard RG, Haugh LD, Reid S, et al. Early prediction of chronic

disability after occupational low-back injury. Spine. 1996;21:945–951.

24

McIntosh G, Frank J, Hogg-Johnson S, et al. Prognostic factors for

time receiving workers’ compensation benefits in a cohort of patients
with low back pain. Spine. 2000;25:147–157.

25

Nordin M, Skovron ML, Hiebert R, et al. Early predictors of delayed

return to work in patients with low-back pain. Journal of Musculoskeletal
Pain. 1997;5:5–27.

26

Fritz JM, George SZ. Identifying psychosocial variables in patients

with acute work-related low back pain: the importance of fear-avoid-
ance beliefs. Phys Ther. 2002;82:973–983.

27

Frank OA, De Souza LH, McAuley JH, et al. A cross-sectional survey

of the clinical and psychological features of low back pain and
consequent work handicap: use of the Quebec Task Force Classifica-
tion. Int J Clin Pract. 2000;54:639 – 644.

28

Werneke MW, Hart DL. Discriminant validity and relative precision

for classifying patients with nonspecific neck and back pain by anatom-
ical pain patterns. Spine. 2003;28:161–166.

29

Donelson R, Silva G, Murphy K, Centralization phenomenon: its

usefulness in evaluating and treating referred pain. Spine. 1990;15:
211–213.

30

Donelson R, Grant W, Kamps C, Medcalf R. Pain response to sagittal

end-range spinal motion: a prospective, randomized, multi-centered
trial. Spine. 1991;16(suppl):S206 –S212.

31

Donelson R, Aprill C, Medcalf R, Grant W. A prospective study of

centralization of lumbar and referred pain: a predictor of symptomatic
discs and annular competence. Spine. 1997;22:1115–1122.

32

Long A. The centralization phenomenon: its usefulness as a predic-

tor of outcome in conservative treatment of low-back pain (a pilot
study). Spine. 1995;20:2513–2521.

33

Razmjou H, Kramer JF, Yamada R. Intertester reliability of the

McKenzie evaluation in assessing patients with mechanical low-back
pain. J Orthop Sports Phys Ther. 2000;30:368 –383.

34

Fritz JM, Delitto A, Vignovic M, Busse RG. Interrater reliability of

judgments of the centralization phenomenon and status change
during movement testing in patients with low-back pain. Arch Phys Med
Rehabil. 2000;81:57– 61.

35

Kilpikoski S, Airaksinen O, Kankaanpaa M, et al. Interexaminer

reliability of low back pain assessment using McKenzie method. Spine.
2002;27:E207–E214.

36

Karas R, McIntosh G, Hall H, et al. The relationship between

nonorganic signs and centralization of symptoms in the prediction of
return to work for patients with low-back pain. Phys Ther. 1997;77:
354 –360.

37

Sufka A, Hauger B, Trenary M, et al. Centralization of low-back pain

and perceived functional outcome. J Orthop Sports Phys Ther. 1998;27:
205–212.

38

Hunt DG, Zuberbier OA, Kozlowski AJ, et al. Are components of a

comprehensive medical assessment predictive of work disability after
an episode of occupational low back trouble? Spine. 2002;27:
2715–2719.

Physical Therapy . Volume 84 . Number 3 . March 2004

Werneke and Hart . 253

ўўўўўўўўўўўўўўўўўўўўўўўўўўўў

39

van der Weide WE, Salle HJ, van Dijk FJ. Prognostic factors for

chronic disability from acute low-back pain in occupational health
care. Scand J Work Environ Health. 1999;25:50 –56.

40

Waddell G. The Back Pain Revolution. Edinburgh, United Kingdom:

Churchill Livingstone; 1998.

41

Fairbank JCT, Couper J, Davies JB, O’Brien JP. The Oswestry low

back pain disability questionnaire. Physiotherapy. 1980;66:271–273.

42

Tate RB, Yassi A, Cooper J. Predictors of time loss after back injury

in nurses. Spine. 1999;24:1930 –1936.

43

Israel BA, House JS, Schurman SJ, et al. The relation of personal

resources, participation, influence, interpersonal relationships and
coping strategies to occupational stress, job strains and health: a
multivariate analysis. Work Stress. 1989;3:163–193.

44

Waddell G, McCulloch JA, Kummel E, Verner RM. Non-organic

physical signs in low-back pain. Spine. 1980;5:117–125.

45

Waddell G, Newton M, Henderson I, et al. A Fear-Avoidance Beliefs

Questionnaire (FABQ) and the role of fear-avoidance beliefs in
chronic low-back pain and disability. Pain. 1993;52:157–168.

46

Derogatis LR. Symptoms Checklist-90: Administration, Scoring and Pro-

cedures Manual for the Revised Version. Baltimore, Md: Clinical Psycho-
metric Research; 1977.

47

Keefe FJ, Wilkins RH, Cook WA. Direct observation of pain behav-

iour in low-back pain patients during physical examination. Pain.
1984;20:59 – 68.

48

Spratt KF, Lehmann TR, Weinstein JN, Sayre HA. A new approach

to low-back physical examination: behavioral assessment of mechanical
signs. Spine. 1990;15:96 –102.

49

Jensen MP, Karoly P, Braver S. The measurement of clinical pain

intensity: a comparison of six methods. Pain. 1986;27:117–126.

50

Selim AJ, Ren XS, Fincke G, et al. The importance of radiating leg

pain in assessing health outcomes among patients with low back pain.
Spine. 1998;23:470 – 474.

51

Kendall FP, McCreary EK. Muscles: Testing and Function. 3rd ed.

Baltimore, Md: Williams & Wilkins; 1983.

52

Nitta H, Tajima T, Sugiyama H, Moriyama A. Study on dermatomes

by means of selective lumbar spinal nerve block. Spine. 1993;13:
1782–1786.

53

Moffett JK, Torgerson D, Bell-Syer S, et al. Randomized controlled

trial of exercise for low back pain: clinical outcomes, costs, and
preferences. BMJ. 1999;319:279 –283.

54

Jensen MP, Turner JA, Romano JM, Ficher LD. Comparative

reliability and validity of chronic pain intensity measures. Pain. 1999;
83:157–162.

55

Cooper JE, Tate RB, Yassi A, Khokhar J. Effect of an early interven-

tion program on the relationship between subjective pain and disabil-
ity measures in nurses with low back injury. Spine. 1996:21:2329 –2336.

56

Von Korff M, Saunders K. The course of back pain in primary care.

Spine. 1996;21:2833–2839.

57

Cohen J. Statistical Power Analysis for the Behavioral Sciences. 2nd ed.

Hillsdale, NJ: Lawrence Erlbaum Associates Inc; 1988:273– 406.

58

Holleman DR, Simel DL. Quantitative assessments from the clinical

examination: how should clinicians integrate the numerous results?
J Intern Med. 1997;12:165–171.

59

Hosmer DW, Lemeshow S. Applied Logistic Regression. New York, NY:

John Wiley & Sons Inc; 1989.

60

Sackett DL, Straus SE, Richardson WS, et al. Evidence-based Medicine:

How to Practice and Teach EBM. 2nd ed. Edinburgh, United Kingdom:
Churchill Livingstone; 2000:67–93.

61

Dujardin B, van den Ende J, van Gompel A, et al. Likelihood ratios:

a real improvement for clinical decision making? Eur J Epidemiol.
1994;10:29 –36.

62

Wainer RS, Fritz JM, Irrgang JJ, et al. Reliability and diagnostic

accuracy of the clinical examination and patient self-report measures
for cervical radiculopathy. Spine. 2003;28:52– 62.

63

Jaeschke R, Guyatt G, Sackett DL. Users’ guides to the medical

literature, III: how to use an article about a diagnostic test, A: are the
results of the study valid? JAMA. 1994;271:389 –391.

64

Jaeschke R, Guyatt G, Sackett DL. Users’ guides to the medical

literature, III: how to use an article about a diagnostic test, B: what are
the results and will they help me in caring for my patients? JAMA.
1994;27:703–707.

65

Altman DG. Diagnostic tests. In: Altman DG, Machin D, Bryant TN,

Gardner MJ, eds. Statistics With Confidence. 2nd ed. Bristol, United
Kingdom: JW Arrowsmith Ltd; 2000:105–119.

66

Sackett DL, Haynes RB, Guyatt GH, Tugwell P. Clinical Epidemiology:

A Basic Science for Clinical Medicine. 2nd ed. Boston, Mass: Little, Brown
and Co Inc; 1992.

67

Hensher D, Johnson LW. Applied Discrete Choice Modeling. London,

United Kingdom: Croom Helm; 1981.

68

Linton SJ. A review of psychological risk factors in back and neck

pain. Spine. 2000;25:1148 –1156.

69

Pincus T, Burton AK, Vogel S, Field AP. A systematic review of

psychological factors as predictors of chronicity/disability in prospec-
tive cohorts of low back pain. Spine. 2002;27:E109 –E120.

70

Turner JA, Franklin G, Turk DC. Predictors of chronic disability in

injured workers: a systematic literature synthesis. Am J Ind Med.
2000;38:707–722.

71

Gatchel RJ, Polatin PB, Mayer TG. The dominant role of psycho-

social risk factors in the development of chronic low back pain
disability. Spine. 1995;20:2702–2709.

72

Waddell G, Somerville D, Henderson I, Newton M. Objective

clinical evaluation of physical impairment in chronic low back pain.
Spine. 1992;17:617– 628.

73

Abenhaim L, Rossignol M, Gobielle D, et al. The prognostic conse-

quences in the making of the initial medical diagnosis of work-related
back injuries. Spine. 1995;20:791–795.

74

Foster NE, Thompson KA, Baxter GD, Allen JM. Management of

nonspecific low-back pain by physiotherapists in Britain and Ireland.
Spine. 1999;24:1332–1342.

254 . Werneke and Hart

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