Frequency of Use of Clinical Trials Registries in Systematic Reviews and Meta-Analyses in Primary Care Journals

Julie Dionne, Lora Cotton, Christopher Thurman, Matt Vassar


Objective: To evaluate the use of clinical trials registries in published primary care systematic reviews and meta-analyses.
Background: Systematic reviews and meta-analyses in primary care medicine that do not report searching for unpublished data may be prone to publication bias. This source of bias occurs when systematic review evidence is based solely on a published body of literature and does not account for studies where results failed to achieve statistical significance and were therefore less likely to be published. One method to address publication bias is to perform a comprehensive search that includes the use of clinical trials registry searches in systematic reviews and meta-analyses published in the top 10 primary care journals over the past 8 years.
Methods: Systematic reviews and meta-analyses were retrieved from the top 10 primary care medicine journals published between January 1st, 2008 and December 31st, 2015 using a highly sensitive search string designed in collaboration with a medical librarian on staff at the Oklahoma State University Center for Health Sciences. We performed a meta-epidemiological study to evaluate the frequency of clinical trials registry searches reported in these systematic reviews and meta-analyses and to evaluate these searches over time.
Results: A total of 205 articles retrieved from PubMed were included for analysis. We found that of the 205 systematic reviews and meta-analyses, only 8.3% (17/205) searched clinical trials registries for unpublished data.
Conclusions: A large portion of systematic reviews and meta-analyses in primary care literature do not search clinical trials registries for unpublished data. Omission of unpublished data from analysis may lead to publication bias and reduced validity of the true effect sizes of interventions.


clinical trials registry, publication bias, systematic review, meta-analysis

Full Text:




Gopalakrishnan S, Ganeshkumar P. Systematic reviews and met-analysis: understanding the best evidence in primary healthcare. Journal of Family Medicine and Primary Care 2013;Jan-Mar 2(1):9-14.

Chou R, Dana T, Blazina I, Daeges M, Bougatsos C, Grusing S, Jeanne TL. Statin use for the prevention of cardiovascular disease in adults: a systematic review for the U.S. Preventive Services Task Force. Evidence Synthesis No. 139. AHRQ Publication No. 14-05206-EF-2. Rockville, MD: Agency for Healthcare Research and Quality 2016.

Dickersin K. The existence of publication bias and risk factors for its occurrence. Journal of the American Medical Association 1990;23:1385-9.

De Angelis C, Drazen JM, Frizelle FA, Haug C, Hoey J, Horton R, et al. Clinical trial registration: a statement from the International Committee of Medical Journal Editors. New England Journal of Medicine 2004;351;1250-1.

Food and Drug Administration Amendments Act of 2007. US Public Law 110-85; 21 USC 301, September 27, 2007.

World Health Organization. WHO statement on public disclosure of clinical trial results. Available at . Retrieved July 12, 2017.

Montori VM, Wilczynski NL, Morgan D, Haynes RB. Optimal search strategies for retrieving systematic reviews from Medline: Analytical Survey. British Medical Journal 2005 Jan 6;330(7482):68.

Montori VM, Wilczynski NL, Morgan D, Haynes RB, et al. Systematic Reviews: A Cross-sectional Study of Locations and Citation Counts. BioMed Central Medicine 2003;1:2.

Crombie IK, Davies HT. What is meta-analysis? evidence-based medicine. April,2009;1-8. Available at . Retrieved March 1, 2016.e2.

Thomson M, Corbin R, Leung L. Effects of ginger for nausea and vomiting in early pregnancy: a meta-analysis. Journal of the American Board of Family Medicine 2014 Jan-Feb;27(1):114-22.

Ding M, Leach M, Bradley H. The effectiveness and safety of ginger for pregnancy-induced nausea and vomiting: a systematic review. Women Birth 2013 Mar;26(1):e26-30.

Bibens ME, Chong AB, Vassar, M. Utilization of clinical trials registries in obstetrics and gynecology systematic reviews. Obstetrics and Gynecology 2016;127 (2):248-53.

Keil LG, Platts-Mills TF, Jones CW. Systematic reviews published in emergency medicine journals do not routinely search clinical trials registries: a cross-sectional analysis. Annals of Emergency Medicine 2015:66:424-27.e2.

Sinnett PM, Carr B, Cook G, Mucklerath H, Varney L, Weiher M, et al. Systematic reviewers in clinical neurology do not routinely search clinical trials registries. Public Library of Science One 2015;10:e0134596.

Jones CW, Keil LG, Weaver MA, Platts- Mills TF. Clinical trials registries are under-utilized in the conduct of systematic reviews: a cross-sectional analysis. Systematic Reviews 2014;3:126.


  • There are currently no refbacks.