Assessment of publication bias in meta-analyses of cardiovascular diseases.

OBJECTIVE To examine variables related with publication bias assessment in a sample of systematic reviews with meta-analysis on cardiovascular diseases. DESIGN Systematic review of meta-analyses. SETTING Journals indexed in Medline and the Cochrane Library. STUDY POPULATION 225 reviews with meta-analysis published between 1990 and 2002. DATA COLLECTION Data from meta-analyses were gathered according to a structured protocol. The outcome was the assessment, not the existence, of publication bias by the original authors. RESULTS Publication bias was assessed in 25 (11.1%) reviews, increasing with time: from 3.4% before 1998 to 19.0% in those published in 2002. A stepwise logistic regression model included several variables increasing the assessment of publication bias: number of primary studies (>7 compared with or=4 compared with <3, OR=8.58, 95% CI=1.73 to 42.62), to be a meta-analysis on observational studies (OR=3.60, 95% CI=1.04 to 12.49), and year of publication (2002 compared with <2000, OR=5.73, 95% CI=1.16 to 28.36). In reviews published in the Cochrane Library publication bias was less frequently assessed (OR=0.06, 95% CI=0.01 to 0.69). CONCLUSIONS The frequency of assessment of publication bias in meta-analysis is still very low, although it has improved with time. It is more frequent in meta-analyses on observational studies and it is related to other methodological characteristics of reviews.