Evidence-appraisal glossary
Interrupted Time Series
A design that tracks an outcome at many time points before and after an intervention, then looks for a shift in the level or slope of the trend at the moment the intervention began. The pre-intervention trend stands in for what would have happened otherwise.
Also called: ITS, segmented regression.
Interrupted time series suits abrupt changes such as a new law, a drug warning, or a screening program. Analysts model the underlying trend and test whether the line jumps up or down (a level change) or bends (a slope change) at the intervention point. Its strength is that each population serves as its own control, but it can be fooled by other events occurring at the same time or by seasonal cycles, so adding a parallel untreated series makes the conclusion far stronger.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.