Time-series study overview — Interrupted time-series study

Question

Define the population-level intervention and outcome whose trajectory is expected to change.

Identify intervention and comparison series

Specify intervention timing and any comparator; document why the comparator represents relevant external influences.

Define periods

Choose pre-intervention, transition and post-intervention periods and the expected lag before analysis.

Prepare repeated outcomes

Build repeated outcomes with consistent definitions, denominators and measurement intervals.

Specify impact model

Prespecify impact shape, trend, distribution, serial correlation, seasonality and effect horizon.

Assess alternative explanations

Assess concurrent events, recording changes, alternative trends and the plausibility of continuing the pre-intervention trajectory.

Report

Report observed and counterfactual trajectories with uncertainty, model checks and attribution limits.

Time-series study overview

End flow

Protocol and decision register

Record the protocol, approvals and registration where applicable. Preserve planned decisions and amendments separately from results.

Protocol and rationale evidence

Attach the rationale and dated protocol, retaining amendments. A study registry records study details; a disease registry contains health data. The HMA–EMA Catalogue of RWD studies is one option for relevant studies. Check eligibility and applicable requirements, and record an identifier and timing if registered. Registration does not imply randomization.