Can We Depend on Investigators to Identify and Register Randomized Controlled Trials?

PURPOSE To reduce publication bias, systematic reviewers are advised to search conference abstracts to identify randomized controlled trials (RCTs) conducted in humans and not published in full. We assessed the information provided by authors to aid identification of RCTs for reviews. METHODS We handsearched the Association for Research in Vision and Ophthalmology (ARVO) meeting abstracts for 2004 to 2009 to identify reports of RCTs. We compared our classification with that of authors (requested by ARVO 2004-2006), and authors' report of trial registration (required by ARVO 2007-2009). RESULTS Authors identified their study as a clinical trial for 169/191 (88%; 95% CI, 84-93) RCTs we identified for 2004, 174/212 (82%; 95% CI, 77-87) for 2005 and 162/215 (75%; 95% CI, 70-81) for 2006. Authors provided registration information for 107/172 (62%; 95% CI, 55-69) RCTs for 2007, 103/153 (67%; 95% CI, 60-75) for 2008, and 126/171 (74%; 95% CI, 67-80) for 2009. Most RCT authors providing a trial register name specified ClinicalTrials.gov (276/312; 88%; 95% CI, 85-92) and provided a valid ClinicalTrials.gov registration number (261/276; 95%; 95% CI, 92-97). Based on information provided by authors, trial registration information would be accessible for 48% (83/172) (95% CI, 41-56) of all ARVO abstracts describing RCTs in 2007, 63% (96/153) (95% CI, 55-70) in 2008, and 70% in 2009 (118/171) (95% CI, 62-76). CONCLUSIONS Authors of abstracts describing RCTs frequently did not classify them as clinical trials nor comply with reporting trial registration information, as required by the conference organizers. Systematic reviewers cannot rely on authors to identify relevant unpublished trials or report trial registration, if present.