According to a study several years ago by the Personal Communications Industry Association, the average cell phone user earns $62,600 per year. Suppose a researcher believes that the average annual earnings of a cell phone user are lower now, and he sets up a study in an attempt to prove his theory. He randomly samples 18 cell phone users and finds out that the average annual salary for this sample is $58,974,with a population standard deviation of $7,810.Use α = .01 to test the researcher’s theory.
Assume wages of cell phone users are normally distributed in the population.