The original meaning of “allocation concealment” is that the statistician and the trial designer who generated the random sequence and allocation sequence should not recruit and allocate the participants for the purpose of avoiding selection bias. In the process of generating allocation sequence, combined blinding measures are so called “setting blinding”, for instance, by using “double simulation”. We use a example to describe how to perform an adequate allocation and conceal the sequence, and setting blinding. Another example is used to describe how to report the methods of randomization, allocation concealment and the effect of blinding, etc.
Random allocation to intervention groups remains the best method of ensuring that the groups being compared are similar at the onset of study and of avoiding removing selection bias between groups of patients. The success of randomization depends on two interrelated processes. First, an unpredictable allocation sequence must be generated based on a random procedure. Second, strict implementation of that sequence must be secured through an assignment mechanism called allocation concealment to prevent those involved in a trial from knowing upcoming assignments. Inadequate allocation concealment can lead to clinicians scheduling patient’s assignment and compromising the unpredictable allocation sequence.
ObjectiveTo analyze the current status of the application of randomization methods in randomized controlled trials (RCTs) which have been published in New England Journal of Medicine (NEJM).MethodsRCTs published by NEJM in 2018 were searched and collected. The characteristics of clinical trial design elements and the application status of randomization methods were comprehensively analyzed to distinguish blind trial and non-blind trial, and characteristics of application of randomization methods and selection of allocation concealment mechanisms of non-blind trials were summarized.ResultsA total of 151 RCTs were published in NEJM in 2018, in which blinded trials and non-blinded trials accounted for 75 (49.67%) and 76 (50.33%), respectively. 34 (22.52%) RCTs did not report specific randomization methods, and the remaining 117 (77.48%) reported. Among the latter, stratified block randomization accounted for the main body (72.65%), followed by block randomization (11.11%), minimization method (9.40%), simple randomization method (4.27%) and the others. There was no significant difference in the proportion of reporting or using randomization methods between blind and non-blind trials (P>0.05). In 76 non-blind trials, 38 (50.00%) clearly reported the concealment method of random allocation, among which 37 used the central randomization (97.37%) and 1 used envelope method (2.63%).ConclusionsThe current RCTs published in NEJM still have problems in the selection of randomization methods to be optimized and the transparency of randomization reporting to be improved.