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. 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.

This is an observational study because there was no random assignment of subjects to experimental conditions.
This is an observational study due to the random assignment of subjects to experimental conditions.
This is an experiment because there was no random assignment of subjects to experimental conditions.
This is an experiment due to the random assignment of subjects to experimental conditions.

(b) The article "Sugar-Sweetened Beverage Intake in Adulthood and Adolescence and Risk of Early Onset Colorectal Cancer among Women" analyzed data from 95,464 female registered nurses who participated in a prospective health study over a 25-year period. As part of the study, the nurses reported their consumption of sugar-sweetened beverages using food frequency questionnaires every four years. The study found that nurses who consumed more than two servings of sugar-sweetened beverages had more than twice the risk of colon cancer compared to those who consumed less than one sugar-sweetened beverage per week.

This is an observational study because there was no random assignment of subjects to experimental conditions.
This is an observational study due to the random assignment of subjects to experimental conditions.
This is an experiment because there was no random assignment of subjects to experimental conditions.
This is an experiment due to the random assignment of subjects to experimental conditions.

c) USA TODAY 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.

This is an observational study because there was no random assignment of subjects to experimental conditions.
This is an observational study due to the random assignment of subjects to experimental conditions.
This is an experiment because there was no random assignment of subjects to experimental conditions.
This is an experiment due to the random assignment of subjects to experimental conditions

(d) The article "Acupuncture for Bad Backs: Even Sham Therapy Works" 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 for those who received real acupuncture (groups 2 and 3) and those who received fake acupuncture toothpick pokes.

This is an observational study because there was no random assignment of subjects to experimental conditions.
This is an observational study due to the random assignment of subjects to experimental conditions.
This is an experiment because there was no random assignment of subjects to experimental conditions.
This is an experiment due to the random assignment of subjects to experimental conditions.