EPIDEMIOLOGY-BIOSTATISTICS EXAM Midterm 2004 PRINT YOUR LEGAL NAME:

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1 EPIDEMIOLOGY-BIOSTATISTICS EXAM Midterm 2004 PRINT YOUR LEGAL NAME: Instructions: This exam is 20% of your course grade. The maximum number of points for the course is 1,000; hence, this exam is worth 200 points. There are 20 questions on this exam. Each question is worth 10 points to yield the maximum of 200 points for this exam. For questions 1-10, record the best answer in pencil on the answer sheet provided. For questions 11-20, write your answers in the spaces provided. Submit your exam and your answer sheet as directed after you have completed the exam. 1. Investigators want to know if a new diet can reduce the risk of stroke in adult women. They conduct a RCT assigning one arm to the new diet and the other arm to their routine diet. It is known that smoking and hypertension are strong risk factors for stroke. Table 1 appears below: New Diet Routine Diet (n=500) (n=500) % Smokers % Hypertension % family history of stroke 3 3 Select the best answer: a.) The lack of adult men in the trial affects its internal validity. b.) It is possible that the crude relative risk for new diet vs. routine diet is 1.0. c.) The authors should adjust for hypertension because it is a potential confounder in this trial. d.) The authors should make the two arms comparable for smoking by matching. e.) The smoking-adjusted relative risk for new diet vs. routine diet must be closer to 1.0 than the crude relative risk.

2 PRINT YOUR LEGAL NAME: 2. Researchers want to study Paroxysmal Nocturnal Hemoglobinuria (PNH), a disease with an incidence of about 1 per million per year, which manifests itself during the early adult years. They wonder if there is an association between low birth weight and the later development of PNH. The researchers should conduct a: (Select the best answer.) a.) RCT with low birth weight and normal birth weight as the two arms. b.) Retrospective cohort study with PNH as one arm and no PNH as the other arm. c.) Retrospective cohort study with low birth weight as one arm and normal birth weight as the other arm. d.) Case control study with PNH as cases and subjects without PNH as controls e.) Large case series 3. Public health officials believe that they could prevent 10 cases of Hepatitis C per 5,000 interns over a 10-year period by preventing all of their needle stick injuries. Select the best answer: a.) This is the attributable risk of Hepatitis C due to needle stick injuries in interns. b.) This is the incidence of Hepatitis C in interns with needle stick injuries divided by the incidence of Hepatitis C in interns without needle stick injuries. c.) This is the cumulative incidence of Hepatitis C in interns with needle stick injuries. d.) This is the incidence rate of Hepatitis C in interns with needle stick injuries. e.) This is the prevalence of Hepatitis C in interns with needle stick injuries.

3 PRINT YOUR LEGAL NAME: 4. A RCT of 10,000 adults was conducted to determine if a new anti-platelet medication taken with aspirin is better than aspirin taken alone in subjects with heart disease. The outcome of interest was MI (heart attack). Select the best answer: a.) It is possible that confounding by the new anti-platelet medication could occur. b.) Comparing one arm taking two medications to another arm taking only one medication will likely lead to interaction by the arm taking the two medications. c.) After randomization, the arms will likely be comparable for unknown potential confounders. d.) Table 1 with the baseline characteristics of both study arms should show both the known and unknown potential confounders. e.) Confounding is eliminated by the choice of a RCT. 5. Which statement best describes adjustment? Select the best answer. a.) It s a method to assure there is an equal distribution of potential confounders in study arms. b.) It s used when there is a concern that confounding may lead to an over estimate or an under estimate of the appropriate measure of association. c.) It can offset the effects of subjects not adhering to their assigned protocols. d.) It s a study design method to help prevent confounding. e.) It s useful in calculating interaction. 6. Select the best statement concerning recall bias: a.) It s a bias unique to retrospective cohort studies. b.) It occurs in RCTs when subjects do not recall their assigned protocols. c.) It occurs if the outcome assessment committee is not blinded such that they can recall to which arm the subject was assigned. d.) It occurs when cases and controls know their outcome status and differentially recall their exposure history in a case control study. e.) It occurs when subjects in a case control study differentially recall their disease outcome.

4 PRINT YOUR LEGAL NAME: 7. The Central Limit Theorem (CLT) says that if many random samples of sufficient size are taken from a population, and the means from each sample are calculated and plotted, that the plot will have certain characteristics. Select the best statement. a.) The CLT predicts that the mean of the distribution of sample means will be the population mean. b.) The CLT predicts that the plot of the sample means will be skewed if the population is skewed. c.) The standard deviation of the sampling distribution is only dependent on the standard deviation of the population distribution. d.) The standard deviation of the population distribution is called the standard error of the mean. e.) The standard deviation of the population distribution is interchangeable with the term standard error. 8. Select the best statement: a.) The p value can be used to help predict the probability that the null hypothesis is false. b.) A trial s power equals the probability of a Type II error. c.) A study result with a p value less than alpha must be statistically significant. d.) A study result with a p value less than alpha must be clinically significant. e.) Performing multiple comparisons without adjusting alpha increases the probability of a Type II error.

5 PRINT YOUR LEGAL NAME: 9. A researcher is conducting a prospective cohort study to determine if there is an association between high fiber diets and gallbladder cancer. She is the only investigator and she is not blinded. There is, however, an independent outcomes committee responsible for determining whether a subject develops gallbladder cancer during the study. The researcher is very concerned that subjects not on a high fiber diet might develop colon cancer, a secondary outcome of the study, so she follows them more closely for colon cancer vs. the subjects on the high fiber diet. Select the best statement: a.) By following the subjects not on a high fiber diet more closely, the researcher will eliminate the chance of non-random misclassification of gallbladder cancer. b.) The study is subject to reporting bias if she erroneously estimates the relative risk of colon cancer in subjects on a high fiber diet compared to those that are not. c.) This study is prone to interviewer bias if the researcher misclassifies the amount of fiber in the subjects diets. d.) Selection bias could have occurred if the researcher only selected subjects from a narrow geographical area. e.) Surveillance bias could lead to non-random misclassification of colon cancer. 10. Select the correct statement regarding societal determinants of health. a.) USA citizens have the longest life expectancy of any nation because the USA spends the most money per capita on health care of any nation. b.) Discrepancies of health status between industrialized nations can partly be explained by variations in the social cohesiveness of its citizens. c.) Once the vast majority of a country s population is lifted out of poverty, all of its citizens experience roughly the same health status. d.) Physicians spend most of their time managing the societal determinants of their patients health. e.) The stressor is a more powerful health determinant than the stress response.

6 PRINT YOUR LEGAL NAME: 11. What is meant by an intention-to-treat analysis? 12. How does non-random misclassification bias of outcomes affect study results? 13. A physician initially wants 80% power to detect a true difference of at least 20% between two study arms with alpha set at After further thought, she wants to achieve 90% power to detect a true difference of at least 20%, still keeping alpha at What does she need to do? 14. An author reports that the relative risk of adults having a heart attack while on aspirin compared to placebo is 0.8. This result is statistically significant. The author further reports that the relative risk of skiers having a heart attack while on aspirin compared to skiers on placebo is 0.7. The relative risk of non-skiers having a heart attack while on aspirin compared to non-skiers on placebo is 0.5. The difference between 0.7 and 0.5 is not statistically significant. The author reports that skiing is an effect modifier in this study. Is the author correct? Answer yes or know and then state your reasons to support your answer.

7 PRINT YOUR LEGAL NAME: 15. What is the essential study design difference between a case control study and a retrospective cohort study? 16. The test scores from an exam are normally distributed with a mean of 80%. One standard deviation was 5%. What percent of those taking the exam scored between 75% and 90%? 17. List the two necessary conditions for confounding to occur. 18. What does it mean when an investigator reports that her study result is statistically significant? 19. The 95% confidence interval on a sample mean extends from 5.0 to 10.0 Is it possible that the population mean from which the sample was drawn, the parameter, does not lie somewhere between 5.0 and 10.0? Explain your answer. 20. List two advantages of a prospective cohort study compared to a case control study. THE END