Information obtained in this study involving 72 girls (6-, 9-, and 12-year-olds) documents the facilitating effect of forced verbalization at three age levels. (Author/WY)

The recommendation to use group means when there may be nonindependence among observational units is unduly restrictive. When random factors are properly identified and included in the analysis, the results are identical in balanced analysis of variance designs, irrespective of whether group means or individual observations are employed.…

Sampling experiments were used to assess the Type I error rates of the t test in situations where classes were randomly assigned to groups but analyses were carried out on individual student scores. Even small amounts of between-class variation caused large inflations in the Type I error rate of the t test. (Author/BW)

This paper demonstrates that gain score analysis and analysis of covariance (ANCOVA) will always yield conflicting results unless the slopes of within-group regression lines of posttest on pretest equal one. In Lord's specific hypothetical example, trait instability invalidates the ANCOVA. An analysis that corrects for this problem is…