A few studies published in 2007 claimed health benefits from eating dark chocolate or drinking cocoa. One study found much lower rates of death due to cancer among the Kuna Indians, who live in the San Blas islands of Panama and drink cocoa as their main beverage, compared to residents of mainland Panama (V. Bayard et al., Int. J. Med. Sci., 2007; 4: 53–58).
a. Identify the response variable and the explanatory variable.
b. Was this study an observational study or an experimental study? Explain.
c. Did the design of this study take into account potential lurking variables? If so, explain how. If not, identify a lurking variable that could affect the results.