8.61 To tip or not to tip
A study of tipping behaviors examined the relationship between the color of the shirt worn by the server and whether or not the customer left a tip.15 There were 418 male customers in the study; 40 of the 69 who were served by a server wearing a red shirt left a tip. Of the 349 who were served by a server wearing a different colored shirt, 130 left a tip.
8.61
(a) The explanatory variable is the color of the shirt; it is used to explain whether or not a tip was given. (b) The response variable is whether a tip was given or not; it is the interest of the study. (c) is the true proportion of male customers who would leave a tip for a red-shirt server. is the true proportion of male customers who would leave a tip for a different-colored-shirt server.