High resolution color graphics plots convey information quickly and concisely. The intervention variable is the passage of a mandatory seatbelt law in January, 1983.
Seatbelt laws are often controversial.
Opponents sometimes claim that they do not significantly reduce the number of casualties. Twelve missing values are added to the end of the data set for use in the example. In January 1983, a mandatory seatbelt law took effect. In this example a footnote is used to add a legend to the plot. 2001 SAS Institute Inc. All Rights Reserved.