University of Alberta

STAT 130

ASSIGNMENT 1 T-TOOLS AND DATA TRANSFORMATIONS In this assignment, you will apply the one- and two-sample t-tools in SPSS to examine data about speed limit increases and changes in motor vehicle fatalities. The t-tools that you will consider are only reliable provided the data satisfy some assumptions. You will use some descriptive and graphical tools in SPSS to verify these model assumptions. Speed Limits and Traffic Fatalities In 1995, the U.S. federal government signed into law The National Highway System Designation Act which abolished the federal mandate of 55 miles per hour maximum speed limits on U.S. interstates. The act permitted the individual states (plus the District of Columbia) to establish their own speed limits. In 1996, of the 50 states (plus the District of Columbia), 32 decided to increase speed limits. The purpose of this study is to compare the changes in traffic mortality in the U.S. between the states that held the speed limit vs. those that increased the speed limit. Did the states that increased speed limits have a greater change in traffic fatalities than those who retained their speed limits? The data collected are the number of traffic fatalities on interstates in 1995 and 1996 for each of the 50 U.S. states plus the District of Columbia. The data are from “Report to Congress: The Effect of Increased Speed Limits in the Post-NMSL Era.” National Highway Traffic Safety Administration, February, 1998; available at http://wwwnrd.nhtsa.dot.gov. The link to the report is: http://www-nrd.nhtsa.dot.gov/pdf/nrd-30/NCSA/Rpts/1998/Speedlim.pdf Use the following variables to answer questions 1 – 4: Column Variable Name Description of Variable 1 state U.S. state (including the District of Columbia) 2 increase Speed limit increase in 1996 = 1 (YES) or 0 (NO). 3 fat95 Number of interstate traffic fatalities in 1995 4 fat96 Number of interstate traffic fatalities in 1996 5 percentchg* Percentage change in interstate traffic fatalities from 1995 to 1996 *The variable “percentchg” is calculated as the change in number of interstate fatalities from 1995 to 1996 divided by the number of interstate fatalities in 1995 (times 100). A positive value means that fatalities increased and a negative value means that fatalities decreased. The above data are available in the SPSS file lab1.sav that can be downloaded to your local station from the Statistical Laboratories web site at http://www.stat.ualberta.ca/statslabs/index.htm (click Stat 252 link and Data for Lab 1). The data are not to be printed in your submission.