Groups and follow-up

Align eligibility exposure and observation

Define eligible alternatives at a common decision point. Consider new-user and active-comparator restrictions when clinically appropriate, and avoid immortal time created by classifying people using future treatment or survival.

Flow diagram

Steps

Define eligible source population

Specify criteria, dates, observation coverage and prevalent/new-user choice.

Define exposed and comparator groups

Choose an active or other comparator with explicit rationale.

Align baseline and covariate windows

Measure baseline covariates before exposure assignment.

Align eligibility assignment and time zero

Prevent immortal-time and related timing biases.

Define exposure and follow-up strategies

Specify switching, discontinuation, censoring and competing events.

Review comparability and exclusions

Document selection and data limitations before effect estimation.