Institutional Affiliation: Harvard Kennedy School of Government
|Testing the Validity of the Single Interrupted Time Series Design|
with Katherine Baicker: w26080
Given the complex relationships between patients’ demographics, underlying health needs, and outcomes, establishing the causal effects of health policy and delivery interventions on health outcomes is often empirically challenging. The single interrupted time series (SITS) design has become a popular evaluation method in contexts where a randomized controlled trial is not feasible. In this paper, we formalize the structure and assumptions underlying the single ITS design and show that it is significantly more vulnerable to confounding than is often acknowledged and, as a result, can produce misleading results. We illustrate this empirically using the Oregon Health Insurance Experiment, showing that an evaluation using a single interrupted time series design instead of the randomized contro...