Open Access Research article

Analysis of decisions made in meta-analyses of depression screening and the risk of confirmation bias: A case study

Felicity A Goodyear-Smith1*, Mieke L van Driel234, Bruce Arroll1 and Chris Del Mar4

Author Affiliations

1 Department of General Practice & Primary Health Care, University of Auckland, PB 92019, Auckland 1142, New Zealand

2 Discipline of General Practice, The University of Queensland, Brisbane, QLD, 4029, Australia

3 Department of General Practice and Primary Health Care, Ghent University, Ghent, 9000, Belgium

4 Centre for Research in Evidence-Based Practice, Bond University, Gold Coast, QLD, Australia

For all author emails, please log on.

BMC Medical Research Methodology 2012, 12:76  doi:10.1186/1471-2288-12-76

Published: 12 June 2012



Depression is common in primary care and clinicians are encouraged to screen their patients. Meta-analyses have evaluated the effectiveness of screening, but two author groups consistently reached completely opposite conclusions.


We identified five systematic reviews on depression screening conducted between 2001 and 2009, three by Gilbody and colleagues and two by the United States Preventive Task Force. The two author groups consistently reached completely opposite conclusions. We analyzed two contemporaneous systematic reviews, applying a stepwise approach to unravel their methods. Decision points were identified, and discrepancies between systematic reviews authors’ justification of choices made were recorded.


Two systematic reviews each addressing three research questions included 26 randomized controlled trials with different combinations in each review. For the outcome depression screening resulting in treatment, both reviews undertook meta-analyses of imperfectly overlapping studies. Two in particular, pooled each by only one of the reviews, influenced the recommendations in opposite directions. Justification for inclusion or exclusion of studies was obtuse.


Systematic reviews may be less objective than assumed. Based on this analysis of two meta-analyses we hypothesise that strongly held prior beliefs (confirmation bias) may have influenced inclusion and exclusion criteria of studies, and their interpretation. Authors should be required to declare a priori any strongly held prior beliefs within their hypotheses, before embarking on systematic reviews.

Meta-analysis; Meta-Analysis as Topic; Bias (Epidemiology); Methods; Depression; Mass screening; Social values; Confirmation bias