Table 1: The Cochrane Collaboration’s tool for assessing risk of bias.

Random sequence generation

 Low risk of biasThe investigators describe a random component in the sequence generation process such as referring to a random number table and using a computer random number generator
 High risk of bias The investigators describe a nonrandom component in the sequence generation process. Usually, the description would involve some systematic, nonrandom approach, for example, sequence generated by odd or even date of birth and sequence generated by some rule based on date (or day) of admission
 Unclear risk of bias Insufficient information about the sequence generation process to permit judgement of “Low risk” or “High risk”

Allocation concealment

 Low risk of bias Participants and investigators enrolling participants could not foresee assignment because one of the following, or an equivalent method, was used to conceal allocation: central allocation (including telephone, web-based, and pharmacy-controlled randomization); sequentially numbered drug containers of identical appearance
 High risk of bias Participants or investigators enrolling participants could possibly foresee assignments and thus introduce selection bias, such as allocation based on using an open random allocation schedule (e.g., a list of random numbers); assignment envelopes were used without appropriate safeguards (e.g., if envelopes were unsealed or nonopaque or not sequentially numbered)

Blinding of participants and personnel

 Low risk of bias Anyone of the following: no blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding; Blinding of participants and key study personnel ensured and unlikely that the blinding could have been broken.
 High risk of bias No blinding or incomplete blinding, and the outcome is likely to be influenced by lack of blinding; blinding of key study participants and personnel attempted but likely that the blinding could have been broken