Testing the Validity of the Single Interrupted Time Series Design

52 Pages Posted: 23 Jul 2019

See all articles by Katherine Baicker

Katherine Baicker

University of Chicago - Harris School of Public Policy

Theodore Svoronos

Harvard University - Harvard Kennedy School (HKS)

Multiple version iconThere are 2 versions of this paper

Date Written: July 2019

Abstract

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 controlled trial would have produced large and statistically significant results of the wrong sign. We discuss the pitfalls of the SITS design, and suggest circumstances in which it is and is not likely to be reliable.

Suggested Citation

Baicker, Katherine and Svoronos, Theodore, Testing the Validity of the Single Interrupted Time Series Design (July 2019). NBER Working Paper No. w26080, Available at SSRN: https://ssrn.com/abstract=3423793

Katherine Baicker (Contact Author)

University of Chicago - Harris School of Public Policy ( email )

1155 East 60th Street
Chicago, IL 60637
United States

Theodore Svoronos

Harvard University - Harvard Kennedy School (HKS) ( email )

79 John F. Kennedy Street
Cambridge, MA 02138
United States

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