Campbell-Style Designs
Interrupted Time Series
Repeated observations before and after a policy can show whether its level or trend departs from the prior trajectory.
Page 1 of 7 · Big Picture
The big picture: Interrupted Time Series
Can a level or trend break distinguish policy change from secular time?
Why a policy analyst should care
A visible pre–post change may simply continue an existing trend; multiple time points let investigators distinguish a policy interruption from secular movement.
Follow the idea from the opening question to a practical decision. These are the conceptual moves this module will develop:
1 Question Did a policy interrupt the outcome level or trend?
2 Explore Many pre-periods anchor the expected trajectory
3 Formalize Level and slope changes
4 Transfer Audit an interrupted series
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