Case and control selection

Define cases and sampling frames

The source population links cases to valid controls. Control sampling and index-date assignment precede analysis and determine what the association estimates. Matching is optional and must be reflected in the analysis.

Flow diagram

Steps

Define source population

Identify the population that gives rise to cases.

Ascertain cases

Specify incident/prevalent case definitions, dates and validation.

Specify control sampling

Choose controls from the population that generated the cases. Specify cumulative, incidence-density or other sampling, comparable index dates and eligibility; controls need not be healthy in every respect.

Specify matching if used

Define factors, timing and matching ratio rationale without fixed defaults.

Finalize sampled sets

Retain sampling strata, matched-set identifiers and exclusions.