An observational study found that authors of randomized controlled trials frequently use concealment of randomization and blinding, despite the failure to report these methods.
OBJECTIVE
Readers of randomized controlled trials (RCTs) commonly assume that what was not reported did not occur. We undertook an observational study to determine whether concealment of randomization or blinding was used in RCTs that failed to report these bias-reducing strategies.


METHODS
We recorded the reporting of concealment of randomization and blinding in 105 RCTs. We subsequently contacted the authors and determined if they had used these methodological safeguards.


RESULTS
We successfully obtained data from 98 authors. The authors in the full-text publications of these 98 RCTs failed to report the presence or absence of concealment of randomization in 55%, and the blinding status of participants in 26%, health care providers in 64%, data collectors in 84%, outcome assessors in 83%, and data analysts in 96%. In direct contact, authors frequently reported concealing randomization (96%; 95% confidence interval CI=87-100%), blinding participants (20%; 95% CI=7-41%), blinding health care providers (65%; 95% CI=52-77%), blinding data collectors (65%; 95% CI=53-75%), blinding outcome assessors (79%; 95% CI=69-87%), and blinding data analysts (50%; 95% CI=40-60%), despite not reporting the use of these methodological safeguards in their publications.


CONCLUSIONS
Readers should not assume that bias-reducing procedures not reported in an RCT did not occur.
Devereaux
P J
PJ
Department of Medicine, Department of Clinical Epidemiology and Biostatistics, Faculty of Health Sciences, McMaster University, Room 2C8, 1200 Main Street West, Hamilton, ON, L8N 3Z5, Canada. philipj@mcmaster.ca
Choi
Peter T-L
PT
El-Dika
Samer
S
Bhandari
Mohit
M
Montori
Victor M
VM
Schünemann
Holger J
HJ
Garg
Amit X
AX
Busse
Jason W
JW
Heels-Ansdell
Diane
D
Ghali
William A
WA
Manns
Braden J
BJ
Guyatt
Gordon H
GH
D015982:Bias; D004311:Double-Blind Method; D004812:Epidemiologic Methods; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012108:Research Personnel; D016037:Single-Blind Method; D014956:Writing