Influence of covariates on heterogeneity in Hamilton Anxiety Scale ratings in placebo

Generalized anxiety disorder is a common psychiatric condition that is associated with decreased quality of life and significant disability. Benzodiazepines are anti-anxiety drugs used widely in the treatment of generalized anxiety disorder. This study examines the influence of several variables on benzodiazepine efficacy in generalized anxiety disorder. We performed a systematic review of placebo-controlled randomized controlled trials with benzodiazepines in generalized anxiety disorder. Fifty-eight studies were deemed eligible to include in the meta-analysis. The studies dated from 1977 to 2013 and included over 5400 participants. From each paper, we extracted: benzodiazepine name and dose, dosing regimen, baseline Hamilton Anxiety Scale (HAM-A) score, change in HAM-A score at study endpoint, drop-out rate, year of study publication, diagnostic criteria used, study size, study duration, location, any conflicts of interest and side-effect profile. We then assessed the influence, direct and indirect, of individual variables on the primary outcome (mean difference at endpoint, HAM-A score). Three factors were shown to be associated statistically with change in HAM-A; baseline HAM-A for benzodiazepine arm, baseline HAM-A for the placebo arm, and duration of the study. A higher baseline HAM-A in both arms was associated with a greater mean difference in HAM-A. A shorter study length was also associated with a greater mean difference. The major factors determining benzodiazepine response was baseline anxiety level for the benzodiazepine arm and study duration. In any design of further meta-analyses and clinical trials for generalized anxiety disorder we suggest that these should be considered these as confounding factors