The speed limit on interstate highways in the United States was reduced from 65 to 55 miles per hour in 1976. It was raised back to 65 in 1988; in 1996, individual state governments could decide the limit and many raised it to 75 miles per hour. Proponents and critics of the law have looked at the number of traffic deaths per 1000 miles driven on the highways between 1970 and 1998 to see whether the law affected traffic deaths. What type of design is this?
A) one shot case study
B) pretest-posttest one group design
C) interrupted time series design
D) equivalent time series design

Question

Quizplus · Accepted Answer

This is an interrupted time series design because it examines the impact of a policy change (speed limit laws) over time, before and after the intervention, using continuous data points.

The Speed Limit on Interstate Highways in the United States