Final Exam Practice Questions PDF

2G03 FINAL EXAM PRACTICE QUESTIONS 1. In a state that did not require varicella (chickenpox) vaccination, a boarding school experienced a prolonged outbreak of varicella among its students that began in September and continued through December. To calculate the probability or risk of illness a...

2G03 FINAL EXAM PRACTICE QUESTIONS 1. In a state that did not require varicella (chickenpox) vaccination, a boarding school experienced a prolonged outbreak of varicella among its students that began in September and continued through December. To calculate the probability or risk of illness among the students, which denominator would you use? a. Number of susceptible students at the ending of the period (i.e., June) b. Number of susceptible students at the midpoint of the period (late October/early November) c. Number of susceptible students at the beginning of the period (i.e., September) d. Average number of susceptible students during outbreak e. Number of vaccinated students at the beginning of the period (i.e., September) 2. A group of researchers performed a large (n=20,654) cross-over randomized trial examining the effect of a drug, Tylenol, versus placebo, on self-reported muscle pain. After analyzing the results, they were surprised to see that the group which received Tylenol first (Group A) outperformed the group which received Placebo first (Group B). As a senior scientist, they come to you for advice. What is the most likely explanation of these results? a. Group B may have realized that they are on the Placebo first group because they felt no improvement in their symptoms. b. Adequate randomization was not achieved. c. The washout period may not have been sufficient, so the Tylenol may have some residual benefit when people began the placebo phase. d. A and b e. A, b, and c 3. In a double-blind, randomized, placebo-controlled trial of fish oil on memory, 19% of the participants in the fish oil group forgot to take their daily supplements during the trial. Only 3% of the participants in the placebo group forgot to take their daily supplements. Is this a problem? a. Yes, because you can be sure that fish oils affect short-term memory. b. No, because participants and investigators were blinded to treatment assignment c. No, because randomization balances known and unknown confounders. d. Yes, because this will likely result in an underestimate of the treatment effect of fish oil. e. No, because the 3% non-adherence in the placebo group is small. 4. Suppose that a small, randomized, double-blind study is conducted. Which of the following problems is most likely to be avoided in this study? a. Non-adherence b. Confounding c. Biased estimate of the disease outcome d. Loss to follow-up e. None of the above; all are possible and likely threats 5. A study of 100 injection drug users who tested negative for HIV infection at enrollment had their HIV status re-tested at 3-month intervals over a 2-year follow-up period. All of the participants were followed for the entire 2-year period. None died, and none were lost to follow-up. Which of the following frequency measures of HIV infection can be calculated at the end of the study? a. Prevalence b. Cumulative incidence c. Incidence rate d. All of the above 6. The incidence rate of a nonfatal disease is 500/100,000 person-years. People usually have the disease for 3 years; at which time the disease resolves spontaneously. What is the best estimate of the prevalence of this disease using this information. Assume the population is in steady state. a. 1,500/100,000 person-years b. 1,000/100,000 person-years c. 167/100,000 person-years d. 500/100,000 person-years e. 333/100,000 person-years 7. Which of the following statements best reflects the purpose of conducting a systematic review? a. It is a relatively quick and easy way to conduct and publish a study because it uses data that is readily available b. It uses existing research evidence based on explicit systematic methods which can be used to make decisions c. It focusses on general clinical questions without a specified search strategy d. It is a mandatory component when completing an economic analysis e. To ensure there is sufficient data to perform a meta-analysis 8. Which of the following is an advantage of case-crossover studies? a. Case-crossover studies typically require fewer participants than a traditional cohort design. b. Case-crossover studies use participants as their own controls. c. Case-crossover studies are less prone to confounding bias because participants act as their own controls. d. All of the above 9. Triangulation refers to… a. Compiling evidence from studies using different methods supporting a causal relationship. b. A hypothetical trial that may or may not be feasible, which addresses the question of interest without any features putting it at risk of bias. c. A thought experiment of replicating patients or participants in two worlds—one in which they underwent a certain intervention or had a particular exposure and one in which they did not undergo an intervention or did not have a particular exposure. d. A method to eliminate confounding bias from the study. 10. Two oncologists want to investigate a new laboratory test that identifies colorectal cancer. Dr. A uses the standard test, which has a sensitivity of 90% and a specificity of 96%. Dr. B uses the new test, which is 96% sensitive and 96% specific. a. Dr. A will correctly identify more patients with colorectal cancer. b. Dr. B will correctly identify more patients with colorectal cancer. c. Doctor A and B will correctly identify an equal number of patients with colorectal cancer. 11. A non-randomized study attempts to investigate the effectiveness of mammographic screening for reducing deaths caused by breast cancer. Which of the following will NOT bias the results of the study? a. Confounding by factors that are different between the group of people who were screened and the group of people who were not screened that may also affect their likelihood of dying from breast cancer (i.e., people of higher SES are more likely to be screened and less likely to die from breast cancer) b. Selection bias (i.e., people who choose to undergo screening are healthier than those who choose not to undergo screening) c. Lead time bias (i.e., screening increases the perceived survival time without affecting the course of the disease) d. The people included in the study are not representative of everyone who will be screened. 12. Primary prevention affects: a. The mortality rate of a disease b. The incidence of a disease c. The duration of the disease d. Relapse 13. Which of the following is a disadvantage of Mendelian randomization studies? a. Estimates from Mendelian randomization studies are as equally confounded as observational studies. b. Mendelian randomization studies can only be used to study select outcomes. c. Most exposures cannot be studied in Mendelian randomization studies because they do not have appropriate genetic variants for investigation. d. Mendelian randomization studies require longer follow-up than randomized trials. 14. Two Amish communities in Guelph are selected to participate in a study of the pneumonia vaccine. A total of 394 school-aged children between 3 and 15 years old in intervention community are given the pneumonia shot, and 234 school-aged children between 3 and 15 years old in the control community are given the Hepatitis A vaccine. Pneumonia is detected in 48 out of 1394 non-recipients and 11 out of 394 recipients in the community assigned to receive the pneumonia vaccine; and 80 out of 1000 nonrecipients and 16 out of 234 recipients in the community assigned to receive the Hepatitis A vaccine. What is the simple indirect protective effectiveness of the pneumonia vaccine? A. 41% B. 43% C. 51% D. 57% E. None of the above 15. A new test has been developed to diagnose primary angle closure glaucoma (PACG), a disease in which the iris blocks the drainage of the eye through the trabecular meshwork. This new test has been performed in 1,000 patients that had documented PACG (disease positive) on gonioscopy (the gold standard test to evaluate the internal drainage system of the eye) and 1,000 normal persons as controls. The authors found that 900 were correctly  classified as PACG (i.e., 100 false negatives) by the new test, and 950 were correctly labeled as free of disease (i.e., 50 false positives). You have been invited by Doctors Without Borders to lead a team that will apply this test in Cyprus (population: 1,000,000). In this country, only 1% of people (i.e., 10,000 cases) are truly afflicted (i.e., confirmed by gold standard) with PACG. How many true positive cases will the test miss? A. 1,000 b. 1 c. 0 d. 9,000 e. 500 16. No diagnostic test is perfect, so clinicians must know how to interpret information on the performance characteristics of tests. Which one of the following statements about test characteristics is correct? a. The pre-test probability of disease is equal to the accuracy of the test. b. The positive predictive value varies with the prevalence of disease in the population being tested. c. The sensitivity varies with the prevalence of disease in the population being tested. d. A highly sensitive test is the best for ruling in disease. e. A highly specific test is best for ruling out disease. 17. You apply a new test to serum taken from 200 horses to detect infection with a virus. Test results were positive in 60 of these horses but only 40 of the 60 were found to harbour the virus when viral cultures were performed (viral isolation is considered to be the Gold Standard). When samples were cultured from test negative horses, 10 returned a positive culture. Assume the 200 horses were representative of the population that exists in your practice region. You want to use this test to screen all horses in your practice. What percentage of horses that test positive would you expect to be false positives? A. 87% B. 80% C. 33.3% D. 66.6% 18. In a population of 1,000 cattle tested for Brucella abortus, 5 positives are identified using a perfect test. What is the sensitivity of the test being used? a. 0.5% b. 99.5% c. 100% d. Cannot be determined 19. A vaccine has an efficacy of 80%. Which of the following statements is correct? a. The vaccine only works 80% of the time b. In a vaccinated population, 80% fewer people will contract the disease if they come in contact with the virus c. The vaccine fails 20% of the time e. Those who are vaccinated are five times less likely to contract the disease if they come in contact with the virus. 20. Which of the following is not true of a case-control study? a. If the rare disease assumption is satisfied, the proportion of cases in the study is a good approximation of the prevalence b. If the rare disease assumption is satisfied, the calculated odds ratio is a valid approximation of the risk ratio you would have obtained from a cohort study c. If the rare disease assumption is violated, the odds ratio is not a valid approximation of the risk ratio you would have obtained from a cohort study d. It is often difficult to choose appropriate controls for a case-control study 21. From a case-control study of depression (exposure) and persistent suicidal behaviour (outcome), you calculate an odds ratio of 1.53. What is the most correct interpretation of the result of this study? a. Those with persistent suicidal behaviour were 53-times more likely to be depressed than those without persistent suicidal behaviour. b. The odds of someone who is depressed going on to develop persistent suicidal behaviour in the future are 1.53 to 1. c. The risk of persistent suicidal behaviour is 1.53-fold higher in those with depression than in those without depression. d. The odds of persistent suicidal behaviour are 1.53-fold higher in those with depression than in those without depression. 22. If randomization of participants in a randomized controlled trial is done correctly, which of the following is incorrect? a. Each participant has an equal chance of being assigned to either group b. Roughly an equal number of participants will be assigned to each group c. Outcomes will occur at random, and on average, will occur at the same frequency in both groups d. The participants will be similar to one another on all factors except the intervention to which they are assigned 23. The concept of “clinical equipoise” refers to a. the expectation that both treatment and control groups should respond in exactly the same fashion to the different treatments b. the assumption that there is not one “better” intervention present (either control or experimental group) during the design of a randomized controlled trial (RCT) c. the assurance that both men and women have equal opportunity to participate in a trial d. the researcher’s certainty that the treatment being tested will work 24. What is the most important reason for blinding in a randomized controlled trial? a. It ensures that the outcome will not be contaminated by non-adherence b. It absolves the investigative team from responsibility, should any adverse events occur during the trial c. Having the same manufacturer make both placebo and control pills helps to keep the cost of the trial reasonable d. It ensures that the reporting and recording of trial outcomes will not be influenced by the subjective perceptions of the participants or investigative team 25. Why is a planned crossover trial more efficient than a parallel trial? a. Because participants serve as their own control, biological variability is smaller, meaning a smaller sample size is required for the trial b. Because participants are free to take the treatments in the order they prefer, the chances of a carryover effect are negligible c. Because a planned crossover trials requires more participants than a parallel trial, it usually takes less time to recruit the desired sample d. Because only half the participants are assigned to each of the treatments, therefore the trial takes less time to complete 26. Which of the following biases is most likely to undermine confidence in a case-control study? a. Volunteer bias b. Selection bias c. Performance bias d. Recall bias 27. Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians. After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart disease. The relative risk was 0.8, with an associated p-value of 0.001. Assuming no confounding, no selection or information bias, and no confounding, what is the most correct conclusion that follows from this finding? a. Vegetarians were 80% less likely to develop heart disease during 30 years of follow-up compared with non-vegetarians. b. Vegetarians were 20% less likely to develop heart disease during 30 years of follow-up compared with non-vegetarians. c. The researchers should have calculated an odds ratio rather than a relative risk. d. The odds ratio of heart disease compare vegetarians to non-vegetarians was 0.4 28. An “intent-to-treat” analysis of the results of a randomized controlled trial means what? a. The results will always be generalizable to the overall population b. Trial subjects will be analyzed according to the treatment they actually received c. The results exclude participants who did not adhere to treatment assignment d. Trial participants will be analyzed according to the group to which they were initially randomized 29. Which of the following is true about a planned crossover (randomized controlled trial) design? a. A washout period is needed to prevent the effects of one intervention from carrying over to the other intervention b. The design may be used to restore internal validity after an unplanned crossover has occurred c. The design is an efficient means of studying therapies that cure disease d. More participants are needed in comparison to other randomized controlled trial designs 30. Fifty people were invited to the retirement party for a senior professor. Forty people ate the cheese dip and 10 of these 40 people got food poisoning. Two people who did not eat the dip also got food poisoning. What is the attack rate (attack “proportion”) for food poisoning from the cheese dip at this party? a. 0.20 b. 0.25 c. 0.15 d. 0.30 31. Which of the following statements about volunteer bias is false? a. Volunteer bias may arise because people who go for screening are typically more compliant with doctor’s orders b. Volunteer bias can lead to overestimates of the effectiveness of a screening program c. Volunteer bias may arise because people who go for screening are generally less healthy than the average person d. Volunteer bias may occur in observational studies 32. Which of the following is true about the difference between random and systematic error? a. random error is less of a problem in small studies than in large studies b. systematic error can only ever result in overestimation of the true effect or association c. random error tends to reduce precision of estimates d. you can reduce systematic error if the sample is large enough 33. You are in charge of a prospective cohort study to understand predictors of stroke, enrolling 100,000 women and 100,000 men aged 19-40. Women who are taking oral contraceptive pills are monitored more closely for signs of stroke by their family physician, because these pills are believed to increase the risk of stroke. Which type of bias would this be likely to introduce? a. Information bias b. Selection bias c. confounding d. No bias 34. In non-differential misclassification of exposure status, in which direction would you expect the measure of association to be biased? (Hint: the null = 1.0, or no association) a. Away from the null b. Towards the null c. It is impossible to predict d. No bias would be introduced if misclassification is non-differential 35. A new drug used to treat breast cancer has been shown to be safer and more effective than usual care in women with all stages of the disease in Phase I and Phase II trials. Researchers are now conducting a randomized controlled trial to further evaluate the new medication. The American Cancer Society’s guidelines wrote that the results of initial studies were conclusive, and the drug should be given to all women with breast cancer. The Canadian Cancer Society’s guidelines expressed concern about methodological limitations of these trials and remain unconvinced of the drug’s effectiveness. They would like more evidence before recommending the drug to patients. An oncologist who treats primarily women with breast cancer is conflicted about whether to enroll her patients in the trial because some (or all) of them may be assigned to the placebo group and not receive the new drug. Is it ethical for her to enroll her patients in the RCT? a. No, enrolling the patients in the RCT is not ethical. Researchers showed that the new drug was effective in earlier trials, and it is therefore unethical to withhold the new drug from women with breast cancer. b. No, enrolling the patients in the RCT is not ethical. There is still medical uncertainty about the drug’s effectiveness, and it should not be given to patients until doctors know for certain it will work. c. Yes, the doctor can ethically enroll her patients in the RCT because there is still uncertainty among medical decision-makers about the drug’s effectiveness. d. Yes, the doctor can ethically enroll her patients in the RCT because some of them will likely be assigned to the intervention group, giving them access to the new drug. 36. Which of the following is NOT a property of a confounder? a. It is a risk factor for the outcome of interest independent of exposure b. It is associated with the exposure of interest c. It is on the causal pathway between exposure and outcome d. It is not a consequence of the exposure