Which cell phone service has the highest rating? The data in CellRating represent the mean ratings for Verizon, AT&T, T-Mobile, and Sprint in 19 different cities.
a. At the 0.05 level of significance, determine whether there is evidence of a difference in the mean cell rating for the four cell phone services.
b. If appropriate, use the Tukey procedure to determine which cell phone services' mean ratings differ. Again, use a 0.05 level of significance.