A study of fast-food intake is described in the paper “What People Buy From Fast-Food Restaurants” (Obesity [2009]: 1369–1374). Adult customers at three hamburger chains (McDonald’s, Burger King, and Wendy’s) in New York City were approached as they entered the restaurant at lunchtime and asked to provide their receipt when exiting. The receipts were then used to determine what was purchased and the number of calories consumed was determined. In all, 3,857 people participated in the study. The sample mean number of calories consumed was 857 and the sample standard deviation was 677.
a. The sample standard deviation is quite large. What does this tell you about number of calories consumed in a hamburger-chain lunchtime fast-food purchase in New York City?
b. Given the values of the sample mean and standard deviation and the fact that the number of calories consumed can’t be negative, explain why it is not reasonable to assume that the distribution of calories consumed is normal.
c. Based on a recommended daily intake of 2,000 calories, the online Healthy Dining Finder (www.healthydiningfinder.com) recommends a target of 750 calories for lunch. Assuming that it is reasonable to regard the sample of 3,857 fast-food purchases as representative of all hamburger-chain lunchtime purchases in New York City, carry out a hypothesis test to determine if the sample provides convincing evidence that the mean number of calories in a New York City hamburger-chain lunchtime purchase is greater than the lunch recommendation of 750 calories. Use α = 0.01.
d. Would it be reasonable to generalize the conclusion of the test in Part (c) to the lunchtime fast-food purchases of all adult Americans? Explain why or why not.
e. Explain why it is better to use the customer receipt to determine what was ordered rather than just asking a customer leaving the restaurant what he or she purchased.
f. Do you think that asking a customer to provide his or her receipt before they ordered could have introduced a bias? Explain.