Chapter 15, Problem 18P

A researcher records the annual number of serious crimes and the amount spent on crime prevention for several small towns, medium cities, and large cities across the country. The resulting data show a strong positive correlation between the number of serious crimes and the amount spent on crime prevention. However, the researcher suspects that the positive correlation is actually caused by population; as population increases, both the amount spent on crime prevention and the number of crimes will also increase. If population is controlled, there probably should be a negative correlation between the amount spent on crime prevention and the number of serious crimes. The following data show the pattern of results obtained. Note that the municipalities are coded in three categories. Use a partial correlation holding population constant to measure the true relations hip between crime rate and the amount spent on prevention.

Number of

CrimesAmount for

PreventionPopulation

Size 3 6 1 4 7 1 6 3 1 7 4 1 8 11 2 9 12 2 11 8 2 12 9 2 13 16 3 14 17 3 16 13 3 17 14 3