Effect size computation for studies with the classroom as the unit of
analysis. Four research studies assigned classes to treatment conditions and
assessed all of the students with LD in the class on pretest and outcome
measures, but then entered the mean score from one to four selected LD
students into the analysis of variance. While appropriately analyzing treatment
effects at the level of assignment for the F-ratios and p values present in the
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study, the variance reported in the studies is problematic for meta-analysis.
That is because effect sizes at the classroom level will tend to be somewhat
inflated. Had the authors reported the ratio of between-class to within-class
variance (ICC) we could have adjusted the Level-2 variance reported to the total
variance (Level-2 + Level-1) required. Without the ICC report, an alternative for
estimation was found in unmoderated ICC values reported by Hedges and
Hedberg (2007, p. 72). These ICCs were further adjusted based on the
differential ratios of Level-2 to Level-1 units in data sets from which they
were drawn to sample sizes in studies analyzed here. Adjustment of g from
these studies was then calculated: