Assessment of risk of bias in included studies
Two authors independently assessed study quality (BM, FS).
The recommended approach for assessing risk of bias in studies
included in systematic reviews from the Cochrane Handbook
(Higgins 2011) was used. Briefly, a two-part tool was used which
addressed six specific domains for assessment of bias (listed below).
Each domain included one or more specific entries in a “risk of
bias” table. Within each entry, the first part of the tool involved
describing what was reported to have happened in the study. The
second part of the tool involved assigning a judgement relating to
the risk of bias for that entry. This was achieved by answering a
pre-specified question about the adequacy of the study in relation
to the entry, such that a judgement of “yes” indicated a low risk
of bias, “no” indicated a high risk of bias, and “unclear” indicated
unclear or unknown risk of bias.
The categories were as follows:
1. Was the allocation sequence adequately generated?
2. Was allocation adequately concealed?
3. Was knowledge of the allocated interventions adequately
concealed during the study?
4. Were incomplete outcome data adequately addressed?
5. Are reports of the study free of suggestion of selective
outcome reporting?
6. Was the study apparently free of any other problems that
could put it at a risk of bias, for example