We’ve just been contacted by a doctor undertaking a systematic review and he asked, for writing up the search strategy, how far back do our records go. Unfortunately it is not possible to give a definitive answer!
In part this relates to the recent post Journal coverage in Trip where we highlight the nature of incorporating documents. We typically say that the bulk of our content is from the year 2000 onwards. However, as we grab all the RCTs and systematic reviews in PubMed, those are our earliest records. So, we’ve got some systematic reviews and and RCTs from the 1950s (although the definition of these research types may well have changed since then) and our earliest guideline appears to be from the late 1990s!.