In a study of the effects of marijuana on the risk of cancer in oral squamous cells, Rosenblatt et al. (2004) examined 407 recent cases of the cancer from western Washington state. They also randomly sampled 615 healthy people from the same region having similar frequency distributions of age and sex as the cancer cases. They found that a similar proportion of the cancer cases (25.6%) and healthy participants (24.4%) reported ever having used marijuana (odds ratio=0.9; 95% confidence interval, 0.6

a. What name is given to this type of study? Is it an experimental study or an observational study? Explain.

b. Does this study include a control group? Explain.

c. What was the purpose of ensuring that the healthy participants were similar in age and sex to the cancer cases?

d. Can we conclude that marijuana does not cause cancer in oral squamous cells in this population?