Two reviewers independently screened the title and
abstracts against the inclusion criteria. Discrepancies were
resolved by consensus. We retrieved the full text articles of
all of the citations marked as included and of the citations
about which reviewers were unsure. Two reviewers
independently reviewed the print copy of the articles
against the inclusion criteria and completed a standardised
form and guide that had previously been pilot tested.
Disagreements were resolved by consensus and if necessary,
by consultation with a third reviewer. See online
Appendix 2 for a copy of the form used.