Researchers monitored the food and drink intake of 159 healthy black and white adolescents aged 15 to 19. "They found that those who drank the most caffeine-more than 100 milligrams a day, or the equivalent of about four 12-ounce cans, had the highest pressure readings."4 Weight was acknowledged as a possible confounding variable-one whose values are tied in with those of the explanatory variable, and also has an impact on the response.
a. Based on your experience, do people who consume a lot of soft drinks tend to weigh more or less than those who do not?
b. Based on your experience, do people who weigh a lot tend to have higher or lower blood pressures?
c. Explain how consumption of soft drinks could be a confounding variable in the relationship between caffeine and blood pressure.
d. If weight is a possible confounding variable, should adolescents of all weights be studied together, or should they be separated out according to weight?
e. Was this an observational study or an experiment?