The article "Tots' TV-Watching May Spur Attention Problems" (San Luis Obispo Tribune, April 5, 2004) describes a study that appeared in the journal Pediatrics. In this study, researchers looked at records of 2500 children who were participating in a longterm health study. They found that 10% of these children had attention disorders at age 7 and that hours of television watched at age 1 and age 3 was associated with an increased risk of having an attention disorder at age 7.

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

b. Give an example of a potentially confounding variable that would make it unwise to draw the conclusion that hours of television watched at a young age is the cause of the increased risk of attention disorder.