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ANCOVA ((menempatkan skor pre-test atau baseline sebagai kovariat), (untuk…

- - - - “ANCOVA assumes that there is no group difference at pretest. This assumption is warranted if treatment assignment is based on randomization or on the pretest” (van Breukelen, 2005)
    - - ANCOVA addresses a conditional hypothesis. Thus, the question that ANCOVA answers may begin with an untenable assumption, that two participants have equivalent scores at baseline “ (Jamieson, 1999)
    - - When post-test variance decreased (e.g., ceiling effect) difference scores lost power, while the power of regression based methods (analysis of covariance and partial correlations) and structural equation measures of change were unaffected “ (Cribbie & Jamieson, 2004)
- - - - “The analysis of gain scores is always appropriate, and that ANCOVA will bias results in non-equivalent groups or observational designs” (Fitzmaurice, Laird, & Ware, 2004)
    - - Equal change between repeated pretests of treated and control group suggests the use of ANOVA of change rather than ANCOVA” (van Breukelen, 2005).
- - - - “ With the assumption of an equivalent comparison group, an analysis of gain scores should give similar results to an ANCOVA” (Maxwell & Delaney, 1990)
    - - It is critically important to use reliable measures and precisely measure variables consistently across subjects and over time, especially when using ANCOVA models” (Oakes & Feldman, 2001)
      - In the presence of measurement error, change-score models may be equally or even more powerful” (Fitzmaurice, Laird, & Ware, 2004)..
    - - “The analysis of gain scores answers a different research question than ANCOVA. The analysis of gains, for example, focuses on the improvements from pretest to posttest for whole groups. The gain score, however, tells us precisely how scores changed from pretest to posttest. (Smolkowski, 2010)
      - An ANCOVA, the alternative to gain scores, focuses on differences between the treatment groups at posttest while holding constant pretest differences. The ANCOVA, then, does not inform about the how the groups changed over time (Smolkowski, 2010).
      - “ANCOVA tests the hypothesis of equivalence of adjusted means, assuming the groups were equivalent on the pretest.…ANOVA on difference scores tests the hypothesis of equivalence of means of differences, regardless of the pretest differences between groups”
    - - Speciﬁcally, for subjects with equal actual change, an easy test (a ceiling effect test) … (or) … a difﬁcult test (a ﬂoor effect test) …. These problems with raw-score differences are eliminated by using modern approaches such as structural equation modeling (Dimitrov & Rumrill, 2003)