The z Test and Starbucks We only use z tests when we have one sample and know the population mean and standard deviation, a rare situation. For example, on average, do people consume fewer calories when they know how many calories are in their favorite latte and muffin? We can use the z test to compare the average numbers of calories that Starbucks customers consume when calorie counts are either posted or not posted on their menu boards.
Donna Ranieri