Carrying out a systematic review of NRS is much more difficult than carrying out a systematic review of randomized trials. It is likely that complex decisions, requiring expert methodological or epidemiological advice, will need to be made at each stage of the review. Potential review authors should therefore seek to collaborate with epidemiologists or methodologists, irrespective of whether a review aims to investigate harms or benefits, short-term or long-term outcomes, frequent or rare events.
Healthcare professionals are keen to be involved in doing reviews of NRS in areas where there are few or no randomized trials because they have the ambition to improve the evidence base in their specialty areas (the motivation for most Cochrane reviews). Methodologists are keen for more systematic reviews of NRS to inform the many areas of uncertainty in methodology highlighted by these chapters. However, healthcare professionals should also recognize that (a) the resources required to do a systematic review of NRS are likely to be much greater than for a systematic review of randomized trials and (b) the conclusions are likely to be much weaker and may make a relatively small contribution to the topic. Therefore, authors and CRG editors need to decide at an early stage whether the investment of resources is likely to be justified by the priority of the research question.
Bringing together the required team of healthcare professionals and methodologists may be easier for systematic reviews of NRS to estimate the effects of an intervention on long-term and rare adverse outcomes, for example when considering the side effects of drugs. However, these reviews may require the input of additional specialist authors, for example with relevant pharmacological expertise. There is a pressing need in many health conditions to supplement traditional systematic reviews of randomized trials of effectiveness with systematic reviews of adverse (unintended) effects. It is likely that these systematic reviews will usually need to include NRS.