MJA
MJA InSight
MJA Careers
EBM: Trials on trial

Allocation concealment and blinding: when ignorance is bliss

Peta M Forder, Val J Gebski and Anthony C Keech
Med J Aust 2005; 182 (2): 87-89.

Good study design involves minimising all possible sources of bias. Two important sources of bias arise through failure to mask (ie, conceal), first, the randomisation process and, second, the treatments after randomisation. Allocation concealment is the term used to describe the procedure for protecting the randomisation process so that the treatment to be allocated is not known before the patient is entered into the study.

Peta M Forder, BSc, MPH, Statistician
Val J Gebski, BA, MStat, Associate Professor, and Senior Research Fellow
Anthony C Keech, FRACP, MScEpid, Deputy Director
NHMRC Clinical Trials Centre, University of Sydney, Sydney, NSW.
Article References: 
Reference Text: 
Altman DG, Schulz KF, Moher D, et al. for the CONSORT Group. The revised CONSORT statement for reporting randomised trials: explanation and elaboration. Ann Intern Med 2001; 134: 663-694.
Reference Order: 
1
PubMed ID: 
11304107
Reference Text: 
Schulz KF, Grimes DA. Allocation concealment in randomised trials: defending against deciphering. Lancet 2002; 359: 614-618.
Reference Order: 
2
PubMed ID: 
11867132
Reference Text: 
Schulz KF, Grimes DA. Blinding in randomised trials: hiding who got what. Lancet 2002; 359: 696-700.
Reference Order: 
3
PubMed ID: 
11879884
Reference Text: 
Sackett DL. Turning a blind eye — why we don’t test for blindness at the end of our trials [letter]. BMJ 2004; 328: 1136.
Reference Order: 
4
PubMed ID: 
15130997
Reference Text: 
Ioannidis JPA, Polycarpou A, Ntais C, Pavlidis N. Randomised trials comparing chemotherapy regimens for advanced non-small cell lung cancer: biases and evolution over time. Eur J Cancer 2003; 39: 2278-2287.
Reference Order: 
5
PubMed ID: 
14556918
Reference Text: 
Schulz KF, Chalmers I, Grimes DA, Altman DG. Assessing the quality of randomisation from reports of controlled trials published in obstetrics and gynecology journals. JAMA 1994; 272: 125-128.
Reference Order: 
6
PubMed ID: 
8015122
Reference Text: 
Dickinson K, Bunn F, Wentz R, et al. Size and quality of randomised controlled trials in head injury: review of published studies. BMJ 2000; 320: 1308-1311.
Reference Order: 
7
PubMed ID: 
10807622
Reference Text: 
Schulz KF, Chalmers I, Altman DG. The landscape and lexicon of blinding in randomized trials. Ann Intern Med 2002; 136: 254-259.
Reference Order: 
8
PubMed ID: 
11827510
Reference Text: 
Kunz R, Oxman AD. The unpredictability paradox: review of empirical comparisons of randomised and non-randomised clinical trials. BMJ 1998; 317: 1185-1190.
Reference Order: 
9
PubMed ID: 
9794851
Reference Text: 
Altman DG, Schulz KF, Moher D. Turning a blind eye — testing the success of blinding and the CONSORT statement [letter]. BMJ 2004; 328: 1135.
Reference Order: 
10
PubMed ID: 
15130995
Reference Text: 
Aspirin Myocardial Infarction Study (AMIS) Research Group. A randomized, controlled trial of aspirin in persons recovered from myocardial infarction. JAMA 1980; 243: 661-669.
Reference Order: 
11
PubMed ID: 
6985998
Reference Text: 
Karloswki TR, Chalmers TC, Frenkel LD, et al. Ascorbic acid for the common cold. A prophylactic and therapeutic trial. JAMA 1975; 231: 1038-1042.
Reference Order: 
12
PubMed ID: 
163386
Reference Text: 
Beller EM, Gebski V, Keech AC. Randomisation in clinical trials. Med J Aust 2002; 177: 565-567. <eMJA full text>
Reference Order: 
13
PubMed ID: 
12429008

The full contents of this page are only available to subscribers.