Detecting the extent of control over selection bias relating to oral health and otorhinolaryngology: cross-sectional study

Abstract

Randomized controlled trials (RCTs) are considered to be a powerful research design for evaluating the effects of healthcare interventions. They constituted one of the most important scientific advances during the 20 th century. Through using such trials, researchers have the assurance that the differences found between the groups evaluated truly result from the effectiveness of the intervention, given that the allocation is random, i.e. there is an equal distribution of prognoses between the groups. 1-3 The controls over the allocation implementation process include generation of a random allocation sequence and simultaneous allocation concealment. 4,5 It is fundamentally important that the investigators should not be capable of anticipating the allocation of the next participants. Absence of controls over the allocation process is a major barrier to internal validity, because this allows the researcher to predict the participants' allocation at the recruitment stage. Even when bias signals are minimal, systematic differences in prognosis can be expected between the groups that will be compared. In particular, selection bias may compromise any randomized experiment in which the enrollment of subjects is sequential and the administration of treatments is unmasked. 6-9 The authors of RCTs will usually claim that they have met the randomization process criterion, in the title of the article or in the abstract. However, sequence generation schemes differ, and some schemes that are claimed to be randomized are not genuinely randomized. 10-13 Even less well understood, and often more difficult to ascertain, is whether the allocation was really concealed. Allocation concealment is actually part of the randomization process and, while distinct from the method used to generate the randomized sequence, is essential to the success of randomization. 13-15