Data extraction
Two authors used pre-designed tables to extract data independently from
each of the eligible studies. Disagreements between the two
investigators were resolved by discussion or consensus with a third
author. We extracted the characteristics of each study and recorded the
following data: first author, year of publication, study design,
characteristics of the study population, sample size and details related
to the methodological quality and results. The numeric results,
statistics used and p values were extracted for each outcome. We
attempted to contact the author of the original report to obtain further
details when the any of the above information was unclear.