6. Interrupted Time Series Analysis

The State of Florida amended self-defense laws in 2005 to provide individuals with legal immunity if they were to use lethal force in self-defense. The intent was to improve public safety and lower the incidence of violent crime. The reverse happened. After the law was enacted, “there was an abrupt and sustained increase in the monthly homicide rate … and in the rate of homicide by firearm.”

Researchers used Interrupted Time Series Analysis (ITSA) to demonstrate the impact of a policy or strategy change where the underlying data set is a time series and not a cross-section.

ITSA is a simple extension of ordinary regression models. It is straightforward to implement and interpret and has been used extensively in the health sector where control and treated groups are used.

Materials:

• • 1. PowerPoint Slides (Click HERE)

    2. Florida Paper (Click HERE)

    3. How to do Policy Analysis (Click HERE).

       1. Lagarde dataset (Click HERE).

    4. Time Series Analysis (Click HERE)

    5. R Code for ITSA for sales tax in California (Click HERE)

• • • 1. Data for Cigarette sales tax in California (Click HERE)

• 1. Resources from Professor Michael Law (UBC)

     1. 1. R Code (Click HERE)

        2. Data Set (Version 1)

        3. Data Set (Version 2)

• • 1. Challenges with Single Group Analysis

       1. Paper by Ariel Linden

       2. Paper by Katherine Baicker and Theodore Svoronos

• 2. Google's Causal Impact (code)

• • • 1. Data in long format

      2. Data in wide format