Chi-square: Cop Deaths

Police officers reduce crime and fear in our communities. Right now, crime is at a 25 year low according to the Department of Justice. The number of police on the street is at an all-time high. However, hundreds of police officers are tragically killed every year in the line of duty. While protecting your rights and safety, some members of the "thin blue line" don't come back to work the next day. You will be performing a chi-square contingency test on data provided by the Department of Justice to determine if officers in different regions are killed more frequently by certain types of weapons. Gun

We can use a Chi-Squared test on a contingency table to determine if there was a significantly different distribution across the nation in the number of officers killed by different types of weapons. In the data, the types of weapons used are classified as handguns, rifles, shotguns, knives, bombs, personal weapons, and others.

Using the data set in Excel, run a Chi-Squared test on a contigency table. In order to use the DIG Stats Online Chi-Squared Calculator, just download either format, open the calculator, and enter the data by hand.

1. What are the values of the Chi-Squared and alpha statistics?
2. Were the different weapons used with the same frequency to kill officers in different areas?
3. Explain how you used the Chi-Squared and alpha statistics to help you arrive at this conclusion.

Original work on this document was done by Central Virginia Governor's School students Richard Barnes, Kim Tibbs, and Ryan Nash (Class of '00).

Copyright © 2011 Central Virginia Governor's School for Science and Technology, Lynchburg, VA