The Environmental Protection Agency wanted to compare the proportion of plants in violation of air quality standards for two different industries: steel and utility. Two independent samples of plants were selected and monitored. The following data was recorded:
Steel: n1=150, number of violations=x1=12
Utility: n2=160, number of violations=x2=12
The null and alternative hypothesis used is:
Ho: p1-p2=0 vs. Ha: p1-p2 not equal 0
Compute the value of the test statistic.