An article appeared in The Wall Street Journal on Tuesday, April 27, 2010, with the title “Eating Chocolate Is Linked to Depression.” The article reported on a study funded by the National Heart, Lung and Blood Institute

(part of the National Institutes of Health) and the University of California, San Diego, that examined 931 adults who were not taking antidepressants and did not have known cardiovascular disease or diabetes. The group was about 70%

men and the average age of the group was reported to be about 58. The participants were asked about chocolate consumption and then screened for depression using a questionnaire.

People who score less than 16 on the questionnaire are not considered depressed and those with scores above 16 and less than or equal to 22 are considered possibly depressed and those with scores above 22 are considered likely to be depressed. The survey found that people who were not depressed ate an average of 5.4 servings of chocolate per month, possibly depressed individuals ate an average of 8.4 servings of chocolate per month, while those individuals who scored above 22 and were likely to be depressed ate the most chocolate, an average of 11.8 servings per month. No differentiation was made between dark and milk chocolate. Other foods were also examined, but no pattern emerged between other foods and depression. Does this type of study establish a cause-and-effect link between chocolate consumption and depression? How would the study have to be conducted to establish such a cause-and effect link?