Table 1 Overview of the broad types of study included in comparative environmental systematic reviews addressing PECO/PICO-type questions (for detail see Additional file 3)

Experimental studies

Randomised controlled experiments

e.g. before-after-control-impact (BACI) studies, control-impact studies, before-after (BA) studies

Non-randomized controlled experiments

Observational studies

Case–control studies

e.g. non-intervention spatial comparison studies

Temporal monitoring studies

e.g. prospective or retrospective time series studies

Cross-sectional studies

e.g. surveys, questionnaires, interviews; studies of spatial occurrence, distribution or prevalence (may be embedded within other study designs)

Other study types

Combined experimental and observational studies

Wide range of designs possible