What is the difference between repeated measures and separate groups in quasi-experimental design?
Repeated measures designs are before-after studies. Separate groups designs use non-equivalent control groups (groups which are matched on identified characteristics but who are not randomly assigned). Since groups are not independent with repeated measures, different calculations must be made. Repeated measures analysis of variance involves violating the ANOVA assumption of independence and therefore requires different computation (ex., how the error terms are computed). SPSS makes different calculations automatically when repeated measures design is specified. Repeated measures ANOVA is also much more affected by violations of the assumption of homogeneity of variances. 3. What is a covariate and how is it used in quai-experimental design? A covariate is simply an interval-level independent which correlates with the dependent. In a quasi-experimental design, the variance of the post-treatment dependent is reduced by the portion accounted for by the covariate. Effects of treatment are
