Question

Exercises (Class and homework) In a study of risk factors for angina (a chronic condition subjects were asked the question, "Do you smoke cigarettes?" Answers were used to classify each respondent as a smoker or nonsmoker. Furthermore, subjects were classified as positive for angina if they had, at some time in the past, been told by a doctor that they had angina. When the resultant data were analyzed, no association was found between cigarette smoking status and angina status A. Has the study measured incidence or prevalence of angina? B. A considerable body of past evidence suggests that the risk of angina increases with increasing tobacco consumption. Suggest reasons why the study described here failed to find an association. C. Suggest an alternative design of study that would be more suitable for investigating whether smoking causes angina. Consider the question(s) that you would ask the chosen subjects about their smoking habits.

Answer 1

Part (a)

The study has only measured the prevalence of angina. Answer

Part (b)

Two factors could have adversely impacted the result of the study.

1. Extent of smoking and severity of the angina

2. Period of smoking and angina incidence.

If these are factored into the study, the result could be corroborating the established link between smoking and angina. Answer

Part (c)

A study design of the following type would factor in the above two factors.

Respondents could be asked to indicate the number of cigarettes they smoked per day during the past, say one year.

And on the incidence of angina again, the respondents could be asked to indicate the angina status as severe, moderate or insignificant.

The response data so obtained need to be cross-tabulated with 4 or 5 classes on the number of cigarettes smoked and 3 classes on the severity of angina.

A chi-square test for association (contingency chi-square) would establish the significance of the association. Answer

DONE