RESEARCHER ALLEGIANCE AND METAANALYSIS - THE CASE OF COGNITIVE THERAPY FOR DEPRESSION

K. S. Dobson (1989) conducted a meta-analysis of 28 studies of cogniti ve-behavioral therapy for depression that used the Beck Depression Inv entory as outcome measure. He concluded that the outcome of this type of therapy was superior to that of other forms of psychotherapy and to that of pharmacotherapy. The present study reanalyzed the same studie s, and a further set of 37 similar ones published from 1987 to 1994, t aking into account variations in sample size and researcher allegiance . This study confirmed Dobson's conclusions for his original sample bu t showed that about half the difference between CT and other treatment s was predictable from researcher allegiance. However, comparable anal yses of the later set of studies showed no effect of researcher allegi ance. Two causes for these phenomena are (a) a historical effect, wher eby both effect sizes and allegiance were large in earlier years and d eclined over time and (b) a treatment effect whereby effect size and a llegiance were correlated, but more for some treatments than others. T his correlation has also weakened over time.