Abstract
Systematic reviews aim to maximise transparency and comprehensiveness, whilst also minimising subjectivity and sources of bias. Because of these time-consuming and complex tasks, systematic reviews are perceived as being resource-intensive. To date, published estimates of systematic review resource requirements have been largely anecdotal, being imprecise and not based on evidence. However, it is valuable to provide reliable means of estimating the resource and time requirements of systematic reviews and maps. We analysed all CEE systematic reviews (n=66) and maps (n=20) published or registered between 2012 and 2017 to estimate the average time needed to complete a systematic review and map. We then surveyed 33 experienced systematic reviewers to collate information on time needed for each stage of the review process. Our results show that the average CEE systematic review takes 157 days (SD; ±22), whilst the average CEE systematic map takes 209 days (SD; ±53). While screening of titles and abstracts is widely accepted to be time-consuming, in practice meta-data extraction and critical appraisal can take as long (or even longer) to complete, especially when producing systematic maps. Finally, we present a tool that allows the user to predict the time requirements of a review or map given information known about the planned methods and evidence base likely to be identified. Our tool uses evidence-based defaults as a useful starting point for those wishing to predict the time requirements for a particular review. Our analyses shed light on the most time-consuming stages of the systematic review and map process, and highlight key bottlenecks from the perspective of time requirements, helping future reviewers to plan their time accordingly. Future predictions of effort required to complete systematic reviews and maps could be improved if CEE and CEE review authors provided more detailed reporting of the methods and results of their reviewing processes.
