In a study similar to that described above for MEDLINE, a search of EMBASE has been carried out by the UK Cochrane Centre for reports of trials not indexed as trials in MEDLINE (Lefebvre 2008). (Trials indexed as such in MEDLINE are already included in CENTRAL as described in Section 6.3.2.1, and are therefore de-duplicated against the EMBASE records as part of the search process.) The following terms are those currently used for the project and have been searched for the years 1980 to 2006: free-text terms: random$; factorial$; crossover$; cross over$; cross-over$; placebo$; doubl$ adj blind$; singl$ adj blind$; assign$; allocat$; volunteer$; and index terms, known as EMTREE terms: crossover-procedure; double-blind procedure; randomized controlled trial; single-blind procedure. A search for the years 1974 to 1979 inclusive has also been completed for the free-text terms: random$; factorial$; crossover$ and placebo$. The $ sign indicates the use of a truncation symbol.
These searches have yielded a total of 80,000 reports of trials not, at the time of the search, indexed as reports of trials in MEDLINE. All of these records are now published in CENTRAL, under contract between Elsevier, the publishers of EMBASE, and The Cochrane Collaboration. Of these 80,000 records, 50,000 are ‘unique’ to CENTRAL, that is they are not already included in CENTRAL with the records sourced from MEDLINE. This search is updated annually. Updates are described in the CENTRAL Creation Details file in The Cochrane Library:
o www3.interscience.wiley.com/cgi-bin/mrwhome/106568753/CENTRALHelpFile.html
and the What’s New section on The Cochrane Library home page:
o www3.interscience.wiley.com/cgi-bin/mrwhome/106568753/HOME