Practice exercises
Part Four: Statistical techniques to explore relationships among variables
You should review the material in the introduction to Part Four and in Chapters 11, 12, 13, 14 and 15 of the SPSS Survival Manual before attempting these exercises.
Correlation
4.1 Using the data file survey.sav follow the instructions in Chapter 11 to explore the relationship between the total mastery scale (measuring control) and life satisfaction (tlifesat). Present the results in a brief report.
4.2 Use the instructions in Chapter 11 to generate a full correlation matrix to check the intercorrelations among the following variables.
(a) age
(b) perceived stress (tpstress)
(c) positive affect (tposaff)
(d) negative affect (tnegaff)
(e) life satisfaction (tlifesat)
4.3 Gill, a researcher, is interested in exploring the impact of age on the experience of positive affect (tposaff), negative affect (tnegaff) and perceived stress (tpstress).
(a) Follow the instructions in Chapter 11 of the SPSS Survival Manual to generate a condensed correlation matrix which presents the correlations between age with positive affect, negative affect and perceived stress.
(b) Repeat the analysis in (a), but first split the sample by sex. Compare the pattern of correlations for males and females. Remember to turn off the Split File option after you have finished this analysis.
Partial correlation
4.4 Follow the procedures detailed in Chapter 12 of the SPSS Survival Manual to calculate the partial correlation between optimism (toptim) and perceived stress (tpstress) while controlling for the effects of age. Compare the zero order correlations with the partial correlation coefficients to see if controlling for age had any effect.
Multiple regression
4.5 There are three main types of multiple regression analyses. What are they? When would you use each approach?
4.6 As part of the preliminary screening process it is recommended that you inspect the Mahalanobis distances produced by SPSS. What do these tell you?
4.7 The example used in the SPSS Survival Manual to demonstrate the use of standard multiple regression compares two control measures (PCOISS and Mastery) in terms of their ability to predict perceived stress. Repeat this analysis, this time using life satisfaction (tlifesat) as your dependent variable. Use the output to answer the following questions.
(a) Overall, how much of the variance in life satisfaction is explained by these two variables?
(b) Which of the independent variables (tpcoiss, tmast) is the best predictor of life satisfaction?
(c) Do both variables make a statistically significant contribution to the prediction of life satisfaction?
4.8 Follow the instructions in the SPSS Survival Manual to perform an hierarchical multiple regression, this time using negative affect as the dependent variable.
Factor analysis
4.10 There is some controversy in the literature concerning the underlying factor structure of one of the scales included in the questionnaire presented in the appendix of the SPSS Survival Manual. The Optimism scale was originally designed as a one-dimension (factor) scale which included some positively worded items and some negatively worded items. Recent studies suggest that it may in fact consist of two factors representing optimism and pessimism.
Conduct a factor analysis using the instructions presented in Chapter 15 to explore the factor structure of the optimism scale (op1 to op6).