QUESTION 3 A study of the impact of needle exchange programs on the transmission of HIV. The needle exchange programs allow drug users to obtain clean needles and syringes free of charge. The investigators are comparing the prevalence of HIV positive cases among injecting drug users in U.S. cities with and without needle-exchange programs. Information on HIV prevalence in each city is being obtained from reports from the Centers for Disease Control and Prevention. Information on the presence or absence of needle exchange programs in each city is being obtained from published reports. What study design is being used? Oa. Cohort study O b. Prospective study Oc. Case-control study Od. Ecological study QUESTION 4 Choose the scenario that comes closest to meeting the ideal counterfactual. Oa. Cannot be determined O b. A study that compares male breast cancer rates among U.S. Marines who were stationed at Camp Lejeune, North Carolina and were exposed to solvents in the local drinking water with breast cancer rates men from the general U.S. population. O c. A study that compares male breast cancer rates among U.S. Marines who were stationed at Camp Lejeune, North Carolina, and were exposed to solvents in the local drinking water with U.S. marines who were stationed at Camp Lejeune, North Carolina but not exposed to solvents in the local drinking water. Od. A study that compares male breast cancer rates among U.S. Marines who were stationed at Camp Lejeune, North Carolina and were exposed to solvents in the local drinking water with U.S. marines who were stationed at Camp Pendleton, California and were not exposed to solvents in the local drinking water.QUESTION 4 Choose the scenario that comes closest to meeting the ideal counterfactual. a. Cannot be determined Ob. A study that compares male breast cancer rates among U.S. Marines who were stationed at Camp Lejeune, North Carolina and were exposed to solvents in the local drinking water with breast cancer rates men from the general U.S. population. Oc. A study that compares male breast cancer rates among U.S. Marines who were stationed at Camp Lejeune, North Carolina, and were exposed to solvents in the local drinking water with U.S. marines who were stationed at Camp Lejeune, North Carolina but not exposed to solvents in the local drinking water. Od. A study that compares male breast cancer rates among U.S. Marines who were stationed at Camp Lejeune, North Carolina and were exposed to solvents in the local drinking water with U.S. marines who were stationed at Camp Pendleton, California and were not exposed to solvents in the local drinking water. QUESTION 5 Suppose that a small, randomized, single-blinded experimental study is conducted with complete data on all participants. Based only on this information, which of the following types of problems are avoided? a. Non-compliance O b. Confounding by known and unknown characteristics Oc. Biased assessment of the outcome Od. Loss-to-follow-up Oe. All of the aboveQUESTION 6 An investigator is interested in studying the impact of air pollution on the risk of coronary heart disease (CHD) among members of a health maintenance organization (HMO) in Northern California. He begins a prospective cohort study in 2002 which includes recruiting 1,250 older men (age 65+ years, including all races) who are free of CHD, measuring air pollution levels at monitoring stations near their homes, and following the men for 10 years (2001-2012). In the analysis, he categorizes the men as having high or low pollution and produces the following two-by-two table: Air Pollution Level High Low Total Yes 400 ?? ? 500 CHD No 600 ?? ? 750 Total ?? ? ?? ? 1,250 What is the relative risk? Notes: 1. Only provide the decimal values. For example: if your answer is 55 per 1,000 people, the input is 0.55. 2. An acceptable range of 0.02 points above or below the answer will be marked correct. Example: If the correct answer is 0.55 and you input 0.56, you will be correct.QUESTION 7 Use the following 2x2 table to calculate the odds ratio: Note: An acceptable range of 0.02 points above or below will be accepted. Group High Level Low Level Cases 520 480 Controls 500 500 QUESTION 8 One way in which cumulative incidence is similar to prevalence is? a. Both measures have denominators that are based on the population at risk for the disease b. Both measures have numerators that are based on new cases of disease O c. Both measures give information about the disease at a snapshot in time d. Both measures are proportions QUESTION 9 Selection bias is most likely to occur in what kind of study design? a. Retrospective cohort studies b. Both retrospective cohort and randomized controlled trials Oc. Case-control studies Od. Experimental studies