Systematic reviews and systematic mapping are evidence synthesis approaches that aim to maximise transparency and comprehensiveness while minimising subjectivity and bias. These are time‐consuming and complex tasks, so systematic reviews are assumed to be resource-intensive; but published estimates of the resources required are largely anecdotal.

The authors analysed all systematic reviews (n = 66) and maps (n = 20) published by the Collaboration for Environmental Evidence (CEE) between May 2012 and March 2017 to estimate the average number of articles retained at each review stage. They also surveyed 33 experienced systematic reviewers to collate information on the rate at which those stages could be completed.

Taken together, the data showed that the average CEE systematic review took around 164 full-time equivalent person-days and the average CEE systematic map (excluding critical appraisal) took 211. While screening titles and abstracts is widely considered time‐consuming, extraction of meta‐data and critical appraisal took as long or longer, especially for systematic maps.

The authors introduce PredicTER, a software tool they have created to predict the time requirements of a systematic review or map, with evidence‐based defaults as a starting point. The results shed light on the most time‐consuming stages of the systematic review and mapping processes, will inform review planning, and can direct innovation to streamline processes.

The article calls on authors of systematic reviews and maps to provide more detail on methods and results, which will facilitate more accurate prediction of the effort involved in future projects.