Background: Systematic reviews (SRs) are important building blocks for clinical practice guidelines and health technology assessment (HTA) reports. With a rapid growth in evidence, it becomes necessary to update SRs regularly to maintain their importance in informing healthcare policy and practice. There is very little guidance available about when and how to update SRs. Moreover, the updating practices of some organizations that commission or produce SRs are unclear.
Objectives: We examined the effect of the time gap between final search and publication of HTA systematic reviews on the usefulness of results and how these can be mitigated for HTA reviews to ensure their up-to-date status. We also examined the consistency in reporting of these reviews using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist.
Methods: We identified and included 14 HTA reviews published from 2005 to 2007. Reviews including at least one randomized trial and at least one meta-analysis were considered. The date of publication, last search date for each review and the date of publication of all the included trials in the review was extracted by dual data extraction. We estimated the probability of trials being missed during the period between the date of last search performed by authors and the date of publication of the review. Each review was also checked against the PRISMA checklist. For reviews where significant numbers of trials had been missed, we repeated the original review searches to identify missed trials, and assessed their impact on results using cumulative meta-analysis.
Results: The study identified that there were several reviews or meta-analyses included in a single report making it difficult to report if updates were required. We will make recommendations for conduct of systematic reviews by the HTA programme and others. Our study will also contribute to understanding best practice for updating systematic reviews.