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Test1: Epidemiology 

1. Consider the following table which summarises the outcome (in terms of survival) for people who have and have not had a heart attack over a five-year follow-up period. In a 2 x 2 table:

	Outcome
Exposure	Dead	Alive
Heart Attack	10	35
No Heart Attack	05	39

 What is the absolute risk of death in each group?
What can you conclude from this result?

2. Consider a cohort study of lung cancer where of a population of 12,000 men, 2000 were exposed to chemical fumes from smelter operations. After 9 years of follow-up 10 cases of lung cancer were observed in the exposed group and 25 cases in the non-exposed group.

What is the relative risk of exposure to chemical fumes for lung cancer?
What can you conclude from this result?

3. Once again, returning to our lung cancer example where 30 of 1000 heavy smokers developed lung cancer over a 10 year period, while 3 of 1000 nonsmokers developed lung cancer over the same period we could draw up the following 2 x 2 table:

	Outcome
Exposure	Lung cancer	No lung cancer
Smoker	30 (a)	9970 (b)
Nonsmoker	03 (c)	9997 (d)

1. What is the Relative Risk?
2. What is the Odds Ratio?
3. What can you conclude from the above results?
4. Are the Relative Risk and Odds Ratio nearly identical in this case?
5. Experiment with the numbers in the 2 x 2 table above. Under what conditions do the the relative risk and odds ratio diverge from each other?