Systematic reviews and meta-analyses on treatment of asthma: critical evaluation.

OBJECTIVE To evaluate the clinical, methodological, and reporting aspects of systematic reviews and meta-analyses on the treatment of asthma and to compare those published by the Cochrane Collaboration with those published in paper based journals. DESIGN Analysis of studies identified from Medline, CINAHL, HealthSTAR, EMBASE, Cochrane Library, personal collections, and reference lists. STUDIES Articles describing a systematic review or a meta-analysis of the treatment of asthma that were published as a full report, in any language or format, in a peer reviewed journal or the Cochrane Library. MAIN OUTCOME MEASURES General characteristics of studies reviewed and methodological characteristics (sources of articles; language restrictions; format, design, and publication status of studies included; type of data synthesis; and methodological quality). RESULTS 50 systematic reviews and meta-analyses were included. More than half were published in the past two years. Twelve reviews were published in the Cochrane Library and 38 were published in 22 peer reviewed journals. Forced expiratory volume in one second was the most frequently used outcome, but few reviews evaluated the effect of treatment on costs or patient preferences. Forty reviews were judged to have serious or extensive flaws. All six reviews associated with industry were in this group. Seven of the 10 most rigorous reviews were published in the Cochrane Library. CONCLUSIONS Most reviews published in peer reviewed journals or funded by industry have serious methodological flaws that limit their value to guide decisions. Cochrane reviews are more rigorous and better reported than those published in peer reviewed journals.