Randomization and concealment in surgical trials: a comparison between orthopaedic and non-orthopaedic randomized trials

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“…This could undermine further the quality of the included randomised controlled trial. With poor methods of concealing the allocation, knowledge of the treatment codes may be gained in advance, increasing the likelihood of selection bias (Li 2005).…”

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“…In two separate studies, RCTs that used inadequate allocation concealment were found to result in an increased estimate of benefit by more than one-third (Schulz et al1995, Moher et al 1998. In an analysis of 29 orthopedic RCTs, 5 did not report the method of concealment (Li et al 2005).…”

“…This limits the possibility of selection bias. Most RCTs rely on sealed envelopes for treatment allocation (Li et al 2005). While sealed envelopes are usually a concealed form of randomization, breach of concealment is possible-and even includes illicit opening and transillumination of sealed envelopes (Schulz 1995).…”