As part of some evaluation efforts on criminal justice reform, Luke Miratrix posted a high level, accessible blog post, "Using Simulation to Analyze Interrupted Time Series", on MDRC's blog Reflections on Methodology on one way to think about analyzing Interrupted Time Series (ITS) designs where you are trying to assess a policy impact for a single unit evolving over time. Be sure to check out the overall blog!  For the evaluation briefs check out the New Jersey report, or the Mecklenberg report.