Some form of a short interrupted time series (ITS) is often used to evaluate state and national programs. An ITS design with a single treatment group assumes that the pretest functional form can be validly estimated and extrapolated into the postintervention period where it provides a valid counterfactual. This assumption is problematic. Ambiguous…

Interrupted time-series (ITS) are often used to assess the causal effect of a planned or even unplanned shock introduced into an on-going process. The pre-intervention slope is supposed to index the causal counterfactual, and deviations from it in mean, slope or variance are used to indicate an effect. However, a secure causal inference is only…

In 2000, Cook, Murphy, and Hunt published a multilevel study of Chicago inner-city schools in order to evaluate James Comer's School Development Program (SDP). One main finding was that SDP reduced the rate of change and final posttest mean when delinquency was assessed annually between Grades 5 and 8 using a self-report measure of acting out. The…