Chapter 9 REPEATED MEASURES ANALYSIS OF VARIANCE REPEATED

Chapter 9 REPEATED MEASURES ANALYSIS OF VARIANCE

REPEATED MEASURES ANOVA o Two major types: n n Measures taken over time Subjects exposed to all levels of the treatment

REPEATED MEASURES o Within Subjects Design n Reduces within group variance Increases F Increases power

REPEATED MEASURES ANOVA o ASSUMPTIONS n Those associated with ANOVA p Categorical independent variable/s p Dependent Variable n n n Normally Distributed Homogeneity of Variance Compound Symmetry p Correlations across all measures are equal p Variances across all measures are equal

Example from the Literature

Exercise o Do people who have never married rate their quality of life (qol) significantly different than married people? o Do people who are rarely depressed rate their qol significantly different than people who are sometimes to routinely depressed? o Do people rate their qol differently now than they did at age 18?

Exercise (continued) o Is there an interaction between marital status and quality of life? o Is there an interaction between level of depression and qol? o Is there an interaction between marital status and depression in relation to qol? o Is there an interaction between marital status, depression, and qol?

Recoded Variables o Marital Status n n n Never married = 0 Married = 1 Everyone else is mssing o Depression n n Rarely = 0 Sometimes to routinely = 1

SPSS - Repeated Measures o ANALYZE n General Linear Model p Repeated n Measures Within Subjects Factor o Name o Number of Levels o Add o Define

Repeated Measures o Plots n Possible Interactions o Options n n Display means Effect Power Homogeneity

Reporting Results for Within. Subjects Factors o Assumption of Compound Symmetry n n If met, report: Tests of Within-Subjects Effects, Sphericity Assumed If not met, report either Tests of Within. Subjects Effects with one of epsilon corrections or the multivariate tests

Epsilon Corrections o Huynh-Feldt n least conservative o Greenhouse-Geisser n conservative o Lower-bound n most conservative

Example o Does satisfaction with life change over time? o IPA 27 - Past o IPA 21 - Present o IPA 29 - Future