Table 1.

Methods for deciphering ^a allocation sequence or otherwise tampering with allocations in randomized trials, based on a systematic review of three empirical studies on the motives and behaviors of investigators recruiting patients to clinical trials

Envelopes/drug containers

• Holding envelopes to light

• Opening envelopes before entering patient

• Entering two patients at the same time, and switching envelopes

• Judging weight difference between envelopes

• When using sequentially numbered drug containers, difference of appearance

Central randomisation

• Several allocations given from central office, at the same time

• Clinician informed of next allocation, before deciding whether to enter the patient

• Manipulation of lists (e.g. not writing patients on lists in the right order)

Others

• Prediction of future assignments based on past assignments, when using restricted randomisation (for example by keeping a log)

• Finding assignment sequence in chief investigators office

^a Some studies employ no allocation concealment, in such cases no deciphering takes place, but the resulting bias remains the same