Search terms were constructed as shown in Fig. S1 (Available in JMM
Online). Searches were performed between 28th and 29th January
2012 and were initially run on the MEDLINE database followed by
the Embase database. Search terms were entered as MeSH terms
rather than text terms. Only articles in the English language were
included in the final list of studies to review. Fig. S1 shows the
number of studies retrieved for each of the search terms and the
methods used to select and reject studies.