The article “Effects of Too Much TV Can Be Undone” (USA Today, October 1, 2007) included the following paragraph: Researchers at Johns Hopkins Bloomberg School of Public Health report that it’s not only how many hours children spend in front of the TV, but at what age they watch that matters. They analyzed data from a national survey in which parents of 2707 children were interviewed first when the children were 30–33 months old and again when they were 5 1 2, about their TV viewing and their behavior. 

a. Is the study described an observational study or an experiment? 

b. The article says that data from a sample of 2707 parents were used in the study. What other information about the sample would you want in order to evaluate the study?