For each of the following, determine whether the statistical study described is an observational study or an experiment. Give a brief explanation of your choice.
a. Can choosing the right music make wine taste better? This question was investigated by a researcher at a university in Edinburgh (www. decanter. com/ news). Each of 250 volunteers was assigned at random to one of five rooms where they were asked to taste and rate a glass of wine. No music was playing in one of the rooms, and a different style of music was playing in each of the other four rooms. The researcher concluded that cabernet sauvignon is rated more highly when bold music is played than when no music is played.
b. The article “ Display of Health Risk Behaviors on MySpace by Adolescents” (Archives of Pediatrics and Adolescent Medicine [ 2009]: 27– 34) described a study of 500 pub-lically accessible MySpace web profiles posted by 18- year- olds. The content of each profile was analyzed and the researchers concluded that those who indicated involvement in sports or a hobby were less likely to have references to risky behavior (such as sexual references or references to substance abuse or violence).
c. USA Today ( January 29, 2003) reported that in a study of affluent Americans ( defined as those with incomes of $ 75,000 or more per year) 57% indicated that they would rather have more time than more money.
d. The article “Acupuncture for Bad Backs: Even Sham Therapy Works” ( Time, May 12, 2009) summarized a study conducted by researchers at the Group Health Center for Health Studies in Seattle. In this study, 638 adults with back pain were randomly assigned to one of four groups. People in group 1 received the usual care for back pain. People in group 2 received acupuncture at a set of points tailored specifically for each individual. People in group 3 received acupuncture at a standard set of points typically used in the treatment of back pain. Those in group 4 received fake acupuncture— they were poked with a toothpick at the same set of points used for the people in group 3. Two notable conclusions from the study were: (1) patients receiving real or fake acupuncture experienced a greater reduction in pain than those receiving usual care; and (2) there was no significant difference in pain reduction between those who received real acu-puncture ( groups 2 and 3) and those who received fake acupuncture toothpick pokes.