Most systematic reviews or meta-analyzes of other studies published in peer reviewed journals or funded by industry have serious methodological flaws that limit their value to guide decisions, say medical researchers.
A team of British medical researchers searched for meta-analyzes or systematic reviews of studies on the treatment of asthma published in peer reviewed journals, the Cochrane Library and medical databases, such as Medline and HealthSTAR.
Meta-analysis is the statistical combination of the results of several independent studies to produce a single estimate of the effect of a particular intervention or health care situation. In the case of asthma, for instance, meta-analysis has been used to evaluate studies on the effects of second-hand cigarette smoke on asthmatics.
The new study looked at the characteristics of the published studies, such as the type of data synthesis used and the quality of the methodology adopted by the studies' authors. Twelve of the reviews were published in the Cochrane Library and 38 were published in 22 peer reviewed journals. Three trained reviewers extracted data independently from the studies and differences were resolved by a fourth reviewer
Source: Alejandro R Jadad, et al., "Systematic reviews and meta-analyses on treatment of asthma: critical evaluation," British Medical Journal, February 27, 2000.
For text http://www.bmj.com/cgi/content/full/320/7234/537