In Example 9.4, assume that it is reasonable to treat the four power plants as a random sample from a large population of power plants, and furthermore, assume that the SO_{2} concentrations in the population of plants are normally distributed. Can we conclude that there are differences in SO_{2} concentrations among the power plants in the population?
This is a random effects model, so we can use the F test to test the null hypothesis that all the treatment means in the population are the same. The results of the F test are shown in Example 9.4. The P-value is 0.006. We therefore reject the null hypothesis and conclude that there are differences in mean SO_{2} concentrations among the power plants in the population.