The instruction should make clear whether the issue is incidence, exposure, relative risk, outbreak analysis or the limits of a study relied upon. An epidemiologist may work alongside clinical, microbiology or occupational-health evidence where a claim requires both population and individual analysis.

• Whether the study design, comparator group and outcome measure support the proposition advanced.
• Whether an association is capable of supporting a causal inference in the circumstances of the case.
• How confounding, bias, sample size and confidence intervals affect the weight that can be placed on the data.
• Whether surveillance, outbreak or exposure data has been interpreted consistently with its stated limitations.
• Where a population-level conclusion ends and a clinician must address individual causation.

Practitioners are listed by discipline and can be narrowed by location across the four UK nations. The register publishes the listing; the instruction is agreed directly with the practitioner.