(1) Random sequence generation (checking for possible
selection bias)
We investigated for each included study the method used to generate
the allocation sequence to allow an assessment of whether it
should produce comparable groups.
We assessed the method as:
• low risk of bias (any truly random process, e.g. random
number table; computer random number generator);
• high risk of bias (any non-random process, e.g. odd or even
date of birth; hospital or clinic record number);
• unclear risk of bias.
(2) Allocation concealment (checking for possible selection
bias)
We investigated for each included study the method used to conceal
allocation to interventions prior to assignment and assessed
whether intervention allocation could have been foreseen in advance
of, or during recruitment, or changed after assignment.