The state and local police departments are trying to analyze crime rates so they can shift their patrols from decreasing-rate areas to areas where rates are increasing. The city and county have been geographically segmented into areas containing 4,550 residences. The police recognize that not all crimes and offenses are reported: people do not want to become involved, consider the offenses too small to report, are too embarrassed to make a police report, or do not take the time, among other reasons. Every month, because of this, the police are contacting by phone a random sample of 910 of the 4,550 residences for data on crime. (Respondents are guaranteed anonymity.) Here are the data collected for the past 12 months for one area: MONTH CRIME INCIDENCE SAMPLE SIZE CRIME RATE
January 11 910 0
February 13 910 0
March 11 910 0
April 11 910 0
May 11 910 0
June 13 910 0
July 11 910 0
August 14 910 0
September 12 910 0
October 15 910 0
November 13 910 0
December 12 910 0
a. Determine the P−P−, Sp, UCL and LCL for a p-chart of 95 percent confidence (at Z = 1.96).
b. If the next three months show crime incidences in this area as
January = 10 (out of 910 sampled)
February = 12 (out of 910 sampled)
March = 11 (out of 910 sampled)
What comments can you make regarding the crime rate?
a. The process is in control.
b. The process is out of control.