Conducting Interrupted Time-series Analysis for Single- and Multiple-group Comparisons

In this article, I introduce the itsa command, which performs interrupted time-series analysis for single- and multiple-group comparisons. In an interrupted time-series analysis, an outcome variable is observed over multiple, equally spaced time periods before and after the introduction of an intervention that is expected to interrupt its level or trend. The itsa command estimates the effect of an intervention on an outcome variable either for a single treatment group or when compared with one or more control groups. Additionally, its options allow the user to control for autocorrelated disturbances and to estimate treatment effects over multiple periods.