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Research design and effect size : a meta-analysis of mood disorder experimental trials Dhaliwal, Lesley


The design of experimental studies can have a significant influence on effect size; however, this influence is rarely given enough consideration during the interpretation and comparison of research results. This paper examines whether there is a significant difference between the effect sizes from placebo-controlled versus treatment-controlled trials. This issue was studied by conducting a meta-analysis of approximately 37 RCTs of mood disorder therapies. The results of this methodological investigation confirmed that there is a statistically significant difference between the weighted effect sizes from the two groups of studies that were compared. These results support the claim that the type of control group is an important factor to consider in the design and interpretation of experimental studies. This analysis is a methodological contribution as it addresses how the type of control group in a RCT impacts the outcome of a study, and more specifically the effect size. The outcome of this research also challenges the effectiveness of treatments that have been tested against only one type of control in experimental studies.

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