Effect size computation for studies with three or four experimental
conditions. Many of the studies in our sample reported outcomes from two or
three experimental conditions, each involving different combinations of
instructional components. We could not compare each condition to the control
group because the set of contrasts would not be orthogonal. We therefore
developed either two or three orthogonal contrasts based on the research
questions posed by the study’s authors. We thus were able to compute two or
three g s that were orthogonal and also addressed a specific research question
(Hedges, personal communication, 2003).
Effect size computation for studies with