Time-series intervention and comparison definition

Specify timing controls and mechanisms

Prespecify the expected intervention mechanism, timing and impact shape. Document concurrent policies and events, and justify any control series. Choosing the interruption date after seeing the outcome can bias interpretation.

Flow diagram

Steps

Specify intervention mechanism

Define the intervention, implementation dates and expected pathway.

Define impact timing

Prespecify immediate, delayed, gradual or temporary effects and anticipation.

Choose comparison design

Document whether a suitable unaffected control series is available.

Identify alternative interruptions

Record concurrent policies, shocks and measurement changes.

Freeze periods and impact question

Define pre/post periods, unit of analysis and target level or trend changes.