PART FIVE: STATISTICAL TECHNIQUES TO COMPARE GROUPS
Before attempting these questions read through the introduction to Part Five and Chapters 16-21 of the SPSS Survival Manual.
T-tests
5.1 Using the data file survey.sav follow the instructions in Chapter 16 of the SPSS Survival Manual to find out if there is a statistically significant difference in the mean score for males and females on the Total Life Satisfaction Scale (tlifesat). Present this information in a brief report.
5.2 Using the data file experim.sav apply whichever of the t-test procedures covered in Chapter 16 of the SPSS Survival Manual that you think are appropriate to answer the following questions.
(a) Who has the greatest fear of statistics at time 1, males or females?
(b) Was the intervention effective in increasing students' confidence in their ability to cope with statistics? You will need to use the variables, confidence time1 (conf1) and confidence time2 (conf2). Write your results up in a report.
(c) What impact did the intervention have on students' levels of depression?
One-way analysis of variance
For exercises 5.3, 5.4 and 5.5, you will need to open the data file survey.sav.
5.3 Perform a one-way between-groups ANOVA to compare the levels of perceived stress (tpstress) for the five different age groups (agegp5), 18-24yrs, 25-32yrs, 33-40yrs, 41-49yrs and 50+yrs.
5.4 Perform post-hoc tests to compare the Self esteem scores (tslfest) for people across the three different age groups (use the agegp3 variable).
For the following exercise you will need to open the data file experim.sav.
5.5 Use one-way repeated measures ANOVA to compare the Fear of Statistics scores for the three time periods (time1, time2 and time3). Inspect the means plots and describe the impact of the intervention and the subsequent follow-up three months later.
Two-way between-groups ANOVA
5.6 For this exercise you will need to open the data file survey.sav. Follow the instructions in Chapter 18 of the SPSS Survival Manual to conduct a two-way ANOVA to explore the impact of sex and age group on levels of perceived stress. The three variables you will need are sex, agegp5 and tpstress.
(a) Interpret the results. Is there a significant interaction effect? Are the two main effects significant?
(b) Write up this analysis and the results in a report. (Don't forget to report the means and standard deviations for each group.)
Mixed between-within subjects analysis of variance
5.7 In Chapter 19 of the SPSS Survival Manual we explored the impact of two different intervention programs (maths skills/confidence building) on participants' fear of statistics. We found that both interventions were equally effective in reducing participants' fear—that is, we found no differences between groups—but a significant difference across the three time periods. Repeat these analyses, but this time use confidence scores as the dependent variable. You will need to use the following variables: group, conf1, conf2 and conf3.
(a) Is there a significant interaction effect between type of intervention (group) and time?
(b) Is there a significant main effect for the within-subjects independent variable, time?
(c) Is there a significant main effect for the between-subjects independent variable, group (maths skills/confidence building)?
Multivariate analysis of variance
5.8 How does MANOVA differ from ANOVA?
5.9 In Chapter 20 of the SPSS Survival Manual it is recommended that you check the Mahalonobis distances before proceeding with MANOVA. What does this allow you to check for?
5.10 Which assumption is Box's Test used to assess?
5.11 Follow the procedure detailed in Chapter 20 of the SPSS Survival Manual to perform a MANOVA to explore positive and negative affect scores for the three age groups (18-29yrs, 30-44yrs, 45+yrs). The three variables you will need are tposaff, tnegaff, agegp3. Remember to check your assumptions first.
Analysis of covariance
5.12 Under what circumstances would you want to consider using analysis of covariance?
5.13 What issues do you need to consider when you are selecting possible covariates?
5.14 Using the experim.sav data file, perform the appropriate analyses (including assumption testing) to compare the confidence scores for the two groups (maths skills, confidence building) at time 2, while controlling for confidence scores at time 1. The variables you will need are group, conf1, conf2.
5.15 Perform a two-way analysis of covariance to explore the question: Does gender influence the effectiveness of the two intervention programs designed to increase participants' confidence in being able to cope with statistics training? You will need to assess the impact of sex and type of intervention (group) on confidence at time 2, controlling for confidence scores at time 1.
Non-parametric statistics
5.16 What is the difference between parametric techniques and non-parametric techniques?
5.17 What factors would you consider when choosing whether to use a parametric or a non-parametric technique?
5.18 For each of the following parametric techniques indicate the non-parametric alternative (if one exists).
(a) one-way between-groups ANOVA
(b) Pearson's product-moment correlation
(c) independent samples t-test
(d) multivariate analysis of variance
(e) one-way repeated measures ANOVA
(f) paired samples t-test
(g) partial correlation
(h) one-way repeated measures ANOVA
5.19 Choose and perform the appropriate non-parametric test to address each of the following research questions.
(a) Using the survey.sav data file find out whether smokers are significantly more stressed than non-smokers. The variables you will need are smoke and total perceived stress (tpstress).
(b) Using the survey.sav data file compare the self-esteem scores across the three different age groups (18-29yrs, 30-44yrs, 45+yrs). The variables you will need are tslfest and agegp3.
(c) Using the survey.sav data file explore the relationship between optimism and negative affect. The variables you will need are toptim and tnegaff.
(d) Using the survey.sav data file explore the association between education level and smoking. The variables you will need are educ2 and smoke. Check the codebook and the questionnaire in the appendix of the SPSS Survival Manual for details on these two variables.
(e) Using the experim.sav data file compare the depression scores at time 1 and the depression scores at time 2. Did the intervention result in a significant change in depression scores? The variables you will need are depress1 and depress2.
(f) Using the experim.sav data file compare the depression scores for the three time periods involved in the study (before the intervention, after the intervention and at the three-month follow up). The variables you will need are depress1, depress2 and depress3.
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