Too little sleep raises obesity risk, reported Mobile Register, November 17, 2005. A study involving about 18,000 adults participating in the federal government's National Health and Nutrition Examination Survey (NHANES) throughout the 1980s. Those who get less than 4 hours of sleep a night were 73% more likely to be obese than those who get the recommended 7-9 hours of rest, scientists discovered.

a Given the brief description presented above, is this a sample survey or an experiment? Why?

b Can we conclude that lack of sleep causes obesity? Justify your answer.