From the discussion:
Of the 90% of our 300 systematic reviews that provided a date of search, the median time from last search to publication was 8.0 months. This is an improvement over the results reported in 2008 where the median time was around 14 months . However, the distribution in our study was skewed, with around 10% of reviews having a last search date to publication time of more than 18 months. Since reviews can date rapidly , this delay is important to users of reviewers.
For a reader searching for an up-to-date review, the relevant date is that of the last search not the date of publication, but this was provided in only 47% of abstracts. Hence readers would need to check, and possibly purchase, the full text to determine recency. Similarly, readers may wish to know the list of databases searched to assess completeness of the review, but this was missing from 40% of abstracts.
The time from search to publication can be usefully compared with the half-life of a review’s conclusions. One analysis of 100 systematic reviews found the half-life was 5.5 years until there was a change in the clinical conclusions of a review . That analysis also found that 7% of reviews were out of date on the day of publication. That is, new research that changed the clinical conclusions was published between the date of search and the date of publication. This is consistent with our finding of a median time from last search to publication delay of 8.0 months.
We found no previous studies on the reporting of dates in abstracts, but several studies have examined the search dates and other items in the full text of reviews. An analysis of 65 Cochrane reviews found that 91% reported the years searched, but only 11% gave the date of last search . Similarly, a study of 297 systematic reviews found that 70% reported the dates covered by the search, and 77% gave the end date of search, but these were better reported in Cochrane reviews (83% and 91%, respectively) than in non-Cochrane reviews (60% and 67%, respectively) .
Beller EM, Chen JK, Wang UL, Glasziou PP. Are systematic reviews up-to-date at the time of publication? Syst Rev. 2013 May 28;2:36. doi: 10.1186/2046-4053-2-36. PMCID: PMC3674908.