Be Sure to Get Your Beauty Sleep! New research supports the idea that people who get a good night's sleep look more attractive. In the study, 23 subjects ages 18 to 31 were photographed twice, once after a good night's sleep and once after being kept awake for 31 hours. Hair, make-up, clothing, and lighting were the same for both photographs. Observers then rated the photographs for attractiveness, and the average rating under the two conditions was compared. The researchers report in the British Medical Journal that "Our findings show that sleep-deprived people appear less attractive compared with when they are well rested."

a. What are the cases?

b. Identify the explanatory and response variables, indicating which one is each, and whether the variable is categorical or quantitative.

The explanatory variable                                                                             is                                                           .

(variable name or description)                (categorical/quantitative)

The response variable                                                                                  is                                                           .

(variable name or description)                   (categorical/quantitative)

c. Is this an observational study, completely randomized experiment, or matched pairs experiment? Explain.