RESEARCH REPORT

Assessment of publication bias in meta-analyses of cardiovascular diseases

Silvia Palma and Miguel Delgado-Rodriguez

Division of Preventive Medicine and Public Health, University of Jaen, Spain

Correspondence to:
Correspondence to:
Professor M Delgado-Rodriguez
Division of Preventive Medicine and Public Health, University of Jaen, 23071-Jaen, Spain; mdelgado{at}ujaen.es

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 7, odds ratio (OR) = 5.40, 95% CI = 1.36 to 21.44), number of searched databases (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.

Keywords: meta-analysis; publication bias; systematic review

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