1. A physical examination was used to screen for breast cancer in 2,500 women with biopsy-proven adenocarcinoma of the breast and in 5,000 age- and race-matched women without cancer. The results of the physical examination were positive (i.e. a mass was found) in 1,800 cases and in 800 non-cases. Calculate the sensitivity and specificity of the physical examination. (Set up your 2x2 table and show your calculations)
   
   
   
2. You now want to go out into a population and screen for breast cancer. Let us say you go to a city with a population of 100,000 women and you estimate the prevalence of breast cancer to be 10%. What is the predictive value (both positive and negative) of the physical examination described in question #1? (Set up your 2x2 table and show your work).
   
   
   
3. A cohort study is conducted to determine the relationship between visual impairment and the risk of injuries from falls among the elderly. A total of 400 visually impaired persons aged 70 or older are compared to 400 persons of comparable age without visual impairment. Over a 5-year follow-up period, 80 visually impaired persons have injuries from falls and 20 non-visually impaired persons have injuries from falls. Calculate the relative risk of falls among elderly visually impaired persons. (Show your work)
   
   
   
4. In an unmatched case-control study of risk factors for congenital defects of the neural tube, maternal deficiency of folate was found in 15 of 100 mothers of cases and 10 of 200 mothers of controls. Calculate the odds of folate deficiency among cases, the odds of folate deficiency among controls, and the odds ratio. (Show your work)

5.  You are a public health official interested in screening for diabetes in your state’s population.  You have recently learned of a newly developed test that produced positive results in 138 of 190 known diabetics and in 24 of 150 persons known not to have diabetes.

a. What is the sensitivity of the new test?

b. What is the specificity of the new test?

c. What is the false-positive rate of the new test?

d. Suppose this test is applied to a population where the estimated prevalence of disease is 10%.  Calculate the positive and negative predictive values of the test.

1. The following scatter plot was created for two characteristics of a sample of automobiles, weight and miles per gallon.  After looking at the graph, what can you conclude about the relationship between the two characteristics?

a. The correlation coefficient is approximately +1.

b. The correlation coefficient is approximately  -1.

c. The correlation coefficient is approximately 0.

d. One can’t estimate the correlation coefficient from the graph.

If there is no correlation between a dependent variable (Y) and an independent variable (X), can one predict Y knowing X?  What is the best guess for Y?

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