2. Ecologic and Cross-sectional studies

a. Describe the basic features of an analytic ecologic study.

b. Assume that the following regression equation was produced by an analysis of results from an ecologic multiple-group study, among 5 counties in Southern part of Florida, of the relationship between per capita alcohol consumption and rates of breast cancer in women:

Y=1.4+0.5x

What is the estimated rate ratio for individuals in this study? How do you interpret this rate ratio?

c. Two epidemiologists wanted to know if heavy cigarette smoking in men (more than two packs per day) is associated with clinical depression. To test their hypothesis, they randomly selected a sample of 149 adult males from Gilford County and initiated an analytic cross-sectional study. The men were queried about current cigarette smoking habits and completed a validated questionnaire designed to measure clinical depression. The results are shown in the following contingency table.

	Clinical Depression	No Clinical Depression
Smokers	20	41
Non-Smokers	18	70

1. Compute and interpret the crude prevalence
2. Calculate and interpret the prevalence odds ratio
3. Calculate the 95% confidence interval and statistical significance for prevalence odds ratio.