Open Access Highly Accessed Research article

Extent of publication bias in different categories of research cohorts: a meta-analysis of empirical studies

Fujian Song12*, Sheetal Parekh-Bhurke2, Lee Hooper1, Yoon K Loke1, Jon J Ryder1, Alex J Sutton3, Caroline B Hing4 and Ian Harvey1

Author Affiliations

1 School of Medicine, Health Policy and Practice, University of East Anglia, Earlham Road, Norwich, NR4 7TJ, UK

2 School of Allied Health Professions, University of East Anglia, Earlham Road, Norwich, NR4 7TJ, UK

3 Department of Health Sciences, University of Leicester, University Road, Leicester, LE1 7RH, UK

4 Watford General Hospital, 60 Vicarage Road, Watford, Hertfordshire, WD18 0HB, UK

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BMC Medical Research Methodology 2009, 9:79  doi:10.1186/1471-2288-9-79

Published: 26 November 2009



The validity of research synthesis is threatened if published studies comprise a biased selection of all studies that have been conducted. We conducted a meta-analysis to ascertain the strength and consistency of the association between study results and formal publication.


The Cochrane Methodology Register Database, MEDLINE and other electronic bibliographic databases were searched (to May 2009) to identify empirical studies that tracked a cohort of studies and reported the odds of formal publication by study results. Reference lists of retrieved articles were also examined for relevant studies. Odds ratios were used to measure the association between formal publication and significant or positive results. Included studies were separated into subgroups according to starting time of follow-up, and results from individual cohort studies within the subgroups were quantitatively pooled.


We identified 12 cohort studies that followed up research from inception, four that included trials submitted to a regulatory authority, 28 that assessed the fate of studies presented as conference abstracts, and four cohort studies that followed manuscripts submitted to journals. The pooled odds ratio of publication of studies with positive results, compared to those without positive results (publication bias) was 2.78 (95% CI: 2.10 to 3.69) in cohorts that followed from inception, 5.00 (95% CI: 2.01 to 12.45) in trials submitted to regulatory authority, 1.70 (95% CI: 1.44 to 2.02) in abstract cohorts, and 1.06 (95% CI: 0.80 to 1.39) in cohorts of manuscripts.


Dissemination of research findings is likely to be a biased process. Publication bias appears to occur early, mainly before the presentation of findings at conferences or submission of manuscripts to journals.