Abstract
The authors of randomized controlled trials will usually claim that they have met the randomization process criterion. However, sequence generation schemes differ and some schemes that are claimed to be randomized are not genuinely randomized. Even less well understood, and often more difficult to ascertain, is whether the allocation was really concealed. To detect the extent of control over selection bias, in a comparison between two Cochrane groups: oral health and otorhinolaryngology; and to describe the methods used to control for this bias. Cross-sectional study conducted in a public university in São Paulo, Brazil. The risk of selection bias in 1,714 records indexed in Medline database up to 2018 was assessed, independent of language and access. Two dimensions implicated in the allocation were considered: generation of the allocation sequence; and allocation concealment. We included 420 randomized controlled trials and all of them were evaluated to detect selection bias. In the sample studied, only 28 properly controlled the selection bias. Lack of control over selection bias was present in 80% of the studies evaluated in both groups. The two groups were similar regarding control over selection bias. They are also similar to the methods used. The dimension of allocation concealment appears to be a limiting factor with regard to production of randomized controlled trials with low risk of selection bias. The quality of reporting in studies on oral health and otorhinolaryngology is suboptimal and needs to be improved, in line with other fields of healthcare.
Highlights
Randomized controlled trials (RCTs) are considered to be a powerful research design for evaluating the effects of healthcare interventions
This was a cross-sectional study in which the risk of selection bias of randomized controlled trials indexed in the Medline database was assessed
The Cochrane strategy combined with the key words in the field of oral health recovered 755 records
Summary
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 20th 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.[1,2,3]. The dimension of allocation concealment appears to be a limiting factor with regard to production of randomized controlled trials with low risk of selection bias. The quality of reporting in studies on oral health and otorhinolaryngology is suboptimal and needs to be improved, in line with other fields of healthcare
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