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Exam 4: Biostatistics

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Question 41

Multiple Choice

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A 65-year-old man with a history of congestive heart failure is hospitalized with chest pain and hypotension requiring admission to the cardiac care unit.  An intra-arterial line is placed for direct blood pressure monitoring.  Consecutive readings of his intra-arterial blood pressure are 75, 110, 80, 90, 75, and 110 mm Hg.  Which of the following represents the median of these blood pressure readings?

A) 80 mm Hg
B) 85 mm Hg
C) 90 mm Hg
D) 100 mm Hg
E) 110 mm Hg

F) A) and E)
G) A) and B)

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Question 42

Multiple Choice

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A new biomarker has been identified that allows for the early detection of invasive gastric carcinoma.  It has a sensitivity of 89% and a specificity of 85% when compared to endoscopy with multiple biopsies.  The test is used in 2 groups: a population in the United States, where 5 out of 100,000 people have gastric cancer, and a population in China, where 100 out of 100,000 people have been diagnosed with the disease.  Which of the following is the most accurate statement concerning this new test?

A) Negative predictive value of the test is lower in the American population
B) Positive predictive value of the test is higher in the Chinese population
C) Sensitivity of the test is higher in the American population
D) Specificity of the test is higher in the Chinese population
E) The test is not reliable in the American population

F) B) and D)
G) C) and D)

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Question 43

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A residency program organized a barbecue at the beginning of the academic year to welcome the new class of first-year residents.  The total number of attendees was 100, including faculty, administrative staff, and residents.  Hamburgers, hotdogs, and potato salad were served.  The following day, 28 of the attendees had diarrhea and vomiting.  All of the attendees were questioned about what they had eaten, and the following table was obtained: Which of the following best describes the attack rate among all of the attendees who had potato salad?

Public health officials involved in developing nutritional guidelines commission a study to determine how dietary eating patterns influence total body iron stores in children age 5-17.  As part of the study, researchers want to assess how 2 independent variables, red meat consumption and egg consumption (both reported in units of ounces/week) , affect serum ferritin concentrations while adjusting for age and gender.  Which of the following statistical techniques is most helpful for determining the association between the study variables?

A suburban hospital is undergoing an annual review by a health care accreditation organization.  As part of the process, iatrogenic infection rates are assessed for all major hospital services.  Inpatient surgical infection statistics for the last year are shown below. What is the case-fatality rate for methicillin-resistant S aureus surgical infections in this hospital?

A study assessed the association between a new vaccine and traveler's diarrhea (TD) .  Researchers selected a random sample of people who intended to travel to regions where they were at increased risk for TD and who had received the new vaccine and another independent random sample of people who intended to travel to the same regions and who had not received the new vaccine.  These 2 samples of travelers were assessed for the occurrence of TD during the trip and for 7 days after returning home.  Which of the following measures of association are the investigators most likely to report?

A study is conducted to assess the relationship between smoking status and forced expiratory volume in one second (FEV₁) .  Subjects are randomly selected and categorized based on smoking status.  Group A consists of 200 nonsmokers, group B consists of 200 light smokers (1-7 cigarettes per day) , group C consists of 200 moderate smokers (8-22 cigarettes per day) , and group D consists of 200 heavy smokers (23+ cigarettes per day) .  FEV₁ is quantitatively measured in all participants using properly calibrated office spirometers.  Which of the following is the most appropriate statistical method to compare the mean FEV₁ results among all 4 groups?

A 34-year-old man is admitted to the hospital with acute chest pain.  An ECG is obtained in the emergency department and shows ST segment elevation in leads II, III, and aVF.  A sample of blood is taken from the patient, and a new test is used to measure plasma homocysteine levels.  The test is repeated 3 times with his blood sample, and the results are 11.8 µmol/L, 9.2 µmol/L, and 13.7 µmol/L (laboratory reference range: 4-14) .  Which of the following parameters is most likely to be low based on the results of the new test?

A prospective study evaluates the relationship between regular antioxidant supplement use (vitamins C and E) and the risk of stroke in healthy and physically active men age 40-60.  The study compares the risk of stroke among men who consumed antioxidant supplements for ≥5 years and among men who consumed antioxidant supplements for <5 years, as compared to a reference group of men who never consumed antioxidant supplements.  According to the study results, men who consumed antioxidant supplements for <5 years and men who consumed antioxidant supplements for ≥5 years have stroke relative risks of 0.95 (p = 0.45) and 0.75 (p < 0.01) , respectively, when compared to the reference group.  The results of the study were adjusted to account for baseline differences related to healthy behaviors and overall health.  Which of the following factors most likely explains why the relative risk of stroke is lower with longer antioxidant use?

The population pyramid of all races and ethnicities for a certain state in the United States is shown below. Which of the following statements best describes the population of this specific state?

An epidemiologist wants to conduct a study on hepatitis C (HCV) transmission in a country with limited healthcare resources.  She has access to a cohort of adults newly diagnosed with HCV and a cohort of age-matched HCV-negative adults.  She plans to use these 2 cohorts of adults to conduct a case-control study.  Which of the following would be the most appropriate measure of interest for this researcher's study?

A group of researchers conducted a case-control study to estimate the association between exposure to a certain pesticide and head and neck squamous cell carcinomas.  Controls were matched to cases by age and gender.  Exposure status was determined by interviewing the subjects.  On matched-pair analysis, the odds ratio is 7.5 (95% confidence interval: 2.3-14.8) .  Based on this information, which of the following is most likely to affect the validity of this study?

A study is conducted to assess whether quantitative measurement of heat shock protein 90 alpha (Hsp90α) in plasma can improve diagnostic accuracy and help monitor treatment response in liver cancer patients.  A total of 300 individuals (100 liver cancer patients and 200 healthy controls) participate in the study.  Analyses reveal that 90 of the liver cancer patients have an abnormally high plasma Hsp90α level and that 12 of the healthy controls have an abnormally high plasma Hsp90α level.  An abnormally high plasma Hsp90α level indicates a positive test for liver cancer.  Which of the following values best represents the specificity of this test?

The aim of a case-control study is to investigate the association between probiotic yogurt intake before and during pregnancy and gestational diabetes mellitus (GDM) in women age >18 during their 24 to 28 weeks of a singleton pregnancy.  The investigators obtain a history of probiotic yogurt intake between cases and controls.  Results of the study are shown below. Which of the following best represents the odds of high probiotic yogurt intake in women with GDM compared to women without GDM?

Researchers conducted a randomized controlled trial to assess the effectiveness of a new drug to reduce severe cutaneous reactions in patients with rheumatoid arthritis who are treated with adalimumab.  Of 150 adults with rheumatoid arthritis who are treated with adalimumab, 75 received the new drug in addition to adalimumab, and 75 received a placebo in addition to adalimumab.  Results show that 6 patients in the new drug group developed severe cutaneous reactions, compared to 9 in the placebo group.  Which of the following represents the relative risk reduction for severe cutaneous reactions among patients in the new drug group?

Officials of a public health department report a higher than normal prevalence of acute myelogenous leukemia (AML) among children age 5-12 in their community.  They observe that some households in the community are exposed to chemical waste from a nearby factory and worry that exposure to this waste is responsible for the increased prevalence of AML.  A case-control study is designed to evaluate the health department officials' claim that exposure to chemical waste is associated with AML in childhood.  Which of the following populations should be selected as the control group?

Plasma homocysteine levels are measured in patients with acute coronary syndrome who are treated at a large community hospital.  The mean plasma homocysteine level in this group is determined to be 11.1 µmol/L with a standard deviation of 1.2 µmol/L.  In a separate group of patients hospitalized on the general ward in the same hospital, the mean plasma level is 9.5 µmol/L and the standard deviation is 1.3 µmol/L.  Which of the following statistical methods should be used to compare the mean homocysteine levels of these 2 groups of patients?

A study is conducted to evaluate the properties of a new test for diagnosing ovarian cancer.  The study enrolled 200 patients who truly have ovarian cancer and 300 patients who truly do not.  Study results showed that the test is 80% sensitive and 70% specific.  Based on this information, which of the following is the approximate number of false negative test results found in this study?

A new test to diagnose urinary tract infections in women is being evaluated.  The comparison gold standard is positive urine dipstick plus urine culture.  Results of the study are given below. What is the new test's specificity?

A group of psychiatrists has noticed an unusual number of older individuals with depression in the surrounding community.  A decision is taken to conduct a cross-sectional study to estimate the prevalence of depression in this specific population.  Estimates for the prevalence of depression (cases per 100 individuals) in the community are as follows: Suppose during an afternoon clinic, a psychiatrist sees a 65-year-old woman, a 72-year-old man, and an 84-year-old woman from this community.  Assuming no relation between the 3 patients, what is the probability that none of them has depression?