Clarifying differences between reviews within evidence ecosystems.

This paper builds on a 2012 paper by the same authors which argued that the types and brands of systematic review do not sufficiently differentiate between the many dimensions of different review questions and review methods (Gough et al., Syst Rev 1:28, 2012). The current paper extends this argument by considering the dynamic contexts, or 'evidence ecosystems', within which reviews are undertaken; the fact that these ecosystems are constantly changing; and the relevance of this broader context for understanding 'dimensions of difference' in the unfolding development and refinement of review methods.The concept of an evidence ecosystem is used to consider particular issues within the three key dimensions of difference outlined in the 2012 paper of (1) review aims and approach, (2) structure and components of reviews, and (3) breadth, depth, and 'work done' by reviews.