New research supports the idea that people who get a good night’s sleep look more attractive. In the study, 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 is the explanatory variable? What is the response variable?

(b) Is this an experiment or an observational study? If it is an experiment, is it a randomized comparative design or a matched pairs design?

(c) Can we conclude that sleep deprivation causes people to look less attractive? Why or why not?