The z Test and Starbucks z tests are conducted in the rare cases in which we have one sample and we know both the mean and the standard deviation of the population. Do people consume fewer mean calories when they know exactly how many calories are in their favorite latte and muffin? The z test allows us to compare average numbers of calories consumed by customers at Starbucks that have calorie counts posted on their menus with average numbers of calories consumed by customers at Starbucks without posted calories.
Donna Ranieri