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Component studies, which involve comparisons between a treatment package and the treatment package without a theoretically important component or the treatment package with an added component, use experimental designs to test whether the component is necessary to produce therapeutic benefit. A meta-analysis was conducted on 27 component studies culled from the literature. It was found that the effect size for the difference between a package with and without the critical components was not significantly different from zero, indicating that theoretically purported important components are not responsible for therapeutic benefits. Moreover, the effect sizes were homogeneous, which suggests that there were no important variables moderating effect sizes. The results cast doubt on the specificity of psychological treatments. It was established in the 1980s that counseling and psychother-apy are remarkably efficacious (Lambert Bergin, 1994; Wam-pold, 2000); now on center stage is the controversy about whether the beneficial effects of counseling and psychotherapy are due to the specific ingredients of the treatments or to the factors common in all therapies (Wampold, 2000). On one side are the advocates of empirically supported treatments who claim that treatments are analogues of medical treatments in that efficacy is attributed to their respective specific ingredients, which are usually presented in
Ahn et al. (Sun,) studied this question.