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Table 1 Elements of a reviewable PICO/PECO question, often structured as “does intervention (I) or exposure (E) applied to populations (P) produces outcome (O) [compared to comparator (C)]?”

From: Systematic searching for environmental evidence using multiple tools and sources

Question element Definition
Population (of subjects) Statistical samples or populations of subject(s) (e.g. ecosystem, species, etc.), to which the intervention will be applied, or exposed to described conditions
Intervention/exposure Policy, action or environmental variable impacting the populations or to which the subject populations are exposed
Comparator What the exposure or intervention are compared to. Either a control with no intervention/exposure or an alternative intervention or a counterfactual scenario
Outcome Consequences of the intervention or exposure. All relevant variables that can be reliably measured