Tips, take 2 In another experiment to see if getting candy after a meal would induce customers to leave a bigger tip, a waitress randomly decided what to do with 80 dining parties. Some parties received no candy, some just one piece, and some two pieces. Others initially got just one piece of candy, and then the waitress suggested that they take another piece. She recorded the tips received, finding that, in general, the more candy, the higher the tip, but the highest tips (23%) came from the parties who got one piece and then were offered more. (“Sweetening the Till: The Use of Candy to Increase Restaurant Tipping,” Journal of Applied Social Psychology 32, no. 2 [2002]: 300–309)

1. Diagram this experiment.

2. How many factors are there? How many levels?

3. How many treatments are there?

4. What is the response variable?

5. Did this experiment involve blinding? Double-blinding?

6. In what way might the waitress, perhaps unintentionally, have biased the results?