Who is blinded in randomized clinical trials? A study of 200 trials and a survey of authors - PubMed
Review
Who is blinded in randomized clinical trials? A study of 200 trials and a survey of authors
Mette Thorlund Haahr et al. Clin Trials. 2006.
Abstract
Background: Insufficient blinding of persons involved in randomized clinical trials is associated with bias. The appraisal of the risk of bias is difficult without adequate information in trial reports.
Purpose: We wanted to study how blinding is reported in clinical trials and how lack of reporting relate to lack of blinding.
Methods: A cohort study of 200 blinded randomized clinical trials published in 2001 randomly sampled from the Cochrane Central Register of Controlled Trials, and a questionnaire survey of the trial authors.
Results: One-hundred and fifty-six (78%) articles described trials as 'double blind'. In three (2%) of such articles the blinding status of patients, health care providers and data collectors was explicitly described. Eighty-eight (56%) articles did not describe the blinding status of any trial person, and 41 articles (26%) reported no blinding relevant information at all beyond the trial being 'double blind'. One-hundred and thirty (65%) surveyed authors responded. Patients were blinded in 101 (97%) 'double blind' trials, and health care providers in 93 (89%). Twenty (19%) 'double blind' trials had not blinded either patients, health care providers or data collectors. Survey responders provided 15 different operational meanings of the term 'double blind', and typically felt that their preferred definition was the most widely used.
Limitations: The proportions in the author survey may be too optimistic due to reporting bias. It is not known how the increased use of the CONSORT guidelines may have affected reporting in years after 2001.
Conclusions: The blinding status of key trial persons was incompletely reported in most randomized clinical trials. Unreported blinding may be frequent, but one of five 'double blind' trials did not blind either patients, treatment providers or data collectors. Authors, referees, and journal editors could improve the completeness of reporting of blinding, eg, by adhering to the CONSORT statement. It is inappropriate to presume blinding of key trial persons based only on the ambiguous term 'double blind'.
Similar articles
-
Hróbjartsson A, Forfang E, Haahr MT, Als-Nielsen B, Brorson S. Hróbjartsson A, et al. Int J Epidemiol. 2007 Jun;36(3):654-63. doi: 10.1093/ije/dym020. Epub 2007 Apr 17. Int J Epidemiol. 2007. PMID: 17440024
-
Devereaux PJ, Choi PT, El-Dika S, Bhandari M, Montori VM, Schünemann HJ, Garg AX, Busse JW, Heels-Ansdell D, Ghali WA, Manns BJ, Guyatt GH. Devereaux PJ, et al. J Clin Epidemiol. 2004 Dec;57(12):1232-6. doi: 10.1016/j.jclinepi.2004.03.017. J Clin Epidemiol. 2004. PMID: 15617948
-
Gummesson C, Atroshi I, Ekdahl C. Gummesson C, et al. J Hand Surg Am. 2004 Jul;29(4):727-34; discussion 735-7. doi: 10.1016/j.jhsa.2004.04.003. J Hand Surg Am. 2004. PMID: 15249101
-
A review of blinding in randomized controlled trials found results inconsistent and questionable.
Boutron I, Estellat C, Ravaud P. Boutron I, et al. J Clin Epidemiol. 2005 Dec;58(12):1220-6. doi: 10.1016/j.jclinepi.2005.04.006. Epub 2005 Sep 30. J Clin Epidemiol. 2005. PMID: 16291465 Review.
-
Blinding terminology used in reports of randomized controlled trials involving dogs and cats.
Giuffrida MA, Agnello KA, Brown DC. Giuffrida MA, et al. J Am Vet Med Assoc. 2012 Nov 1;241(9):1221-6. doi: 10.2460/javma.241.9.1221. J Am Vet Med Assoc. 2012. PMID: 23078571 Review.
Cited by
-
Considerations from the risk of bias perspective for updating Cochrane reviews.
Mayhew AD, Kabir M, Ansari MT. Mayhew AD, et al. Syst Rev. 2015 Oct 6;4:136. doi: 10.1186/s13643-015-0122-3. Syst Rev. 2015. PMID: 26445323 Free PMC article.
-
Moher D, Hopewell S, Schulz KF, Montori V, Gøtzsche PC, Devereaux PJ, Elbourne D, Egger M, Altman DG. Moher D, et al. BMJ. 2010 Mar 23;340:c869. doi: 10.1136/bmj.c869. BMJ. 2010. PMID: 20332511 Free PMC article. No abstract available.
-
de Souza RF, Chaves CA, Nasser M, Fedorowicz Z. de Souza RF, et al. J Appl Oral Sci. 2010 Mar-Apr;18(2):104-9. doi: 10.1590/s1678-77572010000200002. J Appl Oral Sci. 2010. PMID: 20485919 Free PMC article. Review.
-
Scoping review on interventions to improve adherence to reporting guidelines in health research.
Blanco D, Altman D, Moher D, Boutron I, Kirkham JJ, Cobo E. Blanco D, et al. BMJ Open. 2019 May 9;9(5):e026589. doi: 10.1136/bmjopen-2018-026589. BMJ Open. 2019. PMID: 31076472 Free PMC article.
-
Liu SY, Tonggu L, Niu LN, Gong SQ, Fan B, Wang L, Zhao JH, Huang C, Pashley DH, Tay FR. Liu SY, et al. Sci Rep. 2016 Feb 23;6:21882. doi: 10.1038/srep21882. Sci Rep. 2016. PMID: 26903314 Free PMC article. Clinical Trial.
Publication types
MeSH terms
LinkOut - more resources
Full Text Sources