Objectives To study the extent of blinding in randomised clinical trials of psychological interventions and the interpretative considerations if randomised clinical trials are not blinded.
Design Retrospective study of trial reports published in six high impact factor journals within the field of psychiatry in 2017 and 2018.
Setting Trial reports published in World Psychiatry, JAMA Psychiatry, Lancet Psychiatry, American Journal of Psychiatry, British Journal of Psychiatry, or Psychotherapy and Psychosomatics.
Main outcome measures Blinding status of participants, treatment providers, outcome assessors, data managers, the data safety and monitoring committee, statisticians and conclusion makers, if trialists rejected the null hypothesis on the primary outcome measure, and if trialists discussed the potential bias risk from lack of blinding in the published trial report.
Results 63 randomised clinical trials of psychological interventions were identified. None (0%; 95% CI 0% to 5.75%) of the trials reported blinding of all possible key persons. 37 (58.7%; 95% CI 46.42% to 70.04%) trials reported blinding of outcome assessors. Two (3.2%; 95% CI 0.87% to 10.86%) trials reported blinding of participants. Two (3.2%; 95% CI 0.87% to 10.86%) trials reported blinding of data managers. Three (4.8%; 95% CI 1.63% to 13.09%) trials reported blinding of statisticians. None of the trials reported blinding of treatment providers, the data safety and monitoring committee, and conclusion makers. 45 (71.4%; 95% CI 59.30% to 81.10%) trials rejected the null hypothesis on the primary outcome(s). 13 (20.7%; 95% CI 12.48% to 32.17%) trials discussed the potential bias risk from lack of blinding in the published trial report.
Conclusions Blinding of key persons involved in randomised clinical trials of psychological interventions is rarely sufficiently documented. The possible interpretative limitations are only rarely considered. There is a need of randomised clinical trials of psychological interventions with documented blinding attempts of all possible key persons.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
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Contributors SJ, CG, and JCJ initiated the study and wrote the first manuscript draft. SJ and FWF independently retrieved relevant trial reports from the selected databases, performed risk of bias assessments, and statistical analyses with ongoing supervision from CG, SS, IK, and JCJ. All authors read, commented on and approved the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests SS, and FWF receives salaried from the Mental Health Services in the Capital Region of Denmark. SJ, JCJ, and CG receives salaries from the Copenhagen Trial Unit, Centre for Clinical Intervention Research.
Provenance and peer review Not commissioned; externally peer reviewed.
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