Exposure and covariate ascertainment
Measure comparable prior exposure histories
Use comparable exposure windows and ascertainment procedures in cases and controls. Assess recall, recording quality and changes in exposure caused by early symptoms; a lag may reduce but cannot prove removal of reverse causation.
Flow diagram
Steps
Define prior exposure windows
Anchor equivalent exposure windows to comparable reference dates.
Ascertain exposures consistently
Use comparable methods for cases and controls.
Measure confounders and matching factors
Keep causal timing and source definitions explicit.
Assess measurement quality
Evaluate recall, observer and source-related errors; use blinding where appropriate.
Resolve incomplete histories
Prespecify missingness rules without excluding participants ad hoc.
Exposure and covariate ascertainment
End flow
Tables and supporting information
Exposure specification
Define prior exposure consistently.
Measurement checks
Plan comparable ascertainment.