Exam 4: Biostatistics

A research laboratory is evaluating a new dipstick test for diagnosing urinary tract infections (UTIs).  The new test is compared to urinalysis of a midstream urine specimen (considered the diagnostic gold standard) to establish diagnostic test parameters.  The study enrolls 300 patients, of which 100 have a UTI as determined by urinalysis.  The new dipstick test is determined to be 70% sensitive and 90% specific for the diagnosis of UTIs.  How many false positives are present in the study?

An epidemiological study is initiated to assess the impact of type II diabetes mellitus in a large population with little migration.  Disease incidence and prevalence are monitored and recorded as the number of cases per 1,000 individuals over a 30-year period. Which of the following is the most likely explanation for the change in disease prevalence seen in the graph?

A 73-year-old man comes to the office for follow-up.  He was diagnosed with chronic lymphocytic leukemia (CLL) 3 years ago when routine laboratory testing revealed a markedly elevated leukocyte count.  He feels well.  On examination, he has stable lymphadenopathy.  He has been reading about management options should his CLL progress and inquires about an experimental drug that selectively binds malignant lymphocytes.  The drug has been shown to significantly prolong survival in patients with stage 3 and 4 CLL, without curing the malignancy.  If this new drug were widely used, what changes would be expected in the number of incident and prevalent cases of CLL?

A 50-year-old man comes to the physician for a routine check-up.  He has a 20-pack-year smoking history and consumes alcohol occasionally.  He eats a balanced diet and consumes fried foods and red meat several times a week.  He is not very active and spends much of his free time watching television and sitting at his computer.  His family history is significant for hypertension in his mother and bladder cancer in his father.  His blood pressure is 160/90 mm Hg and heart rate is 70/min.  Laboratory testing is significant for a fasting blood glucose level of 155 mg/dL.  Which of the following interventions is likely to have the greatest effect on reducing this patient's mortality risk?

A study is conducted to assess the potential clinical benefit and treatment-related toxicities of tandutinib in combination with bevacizumab for patients with recurrent glioblastoma.  Forty-one recurrent, bevacizumab-naïve glioblastoma patients were recruited for the study.  Treatment consisted of tandutinib 500 mg twice daily and bevacizumab 10 mg/kg every 2 weeks starting day 15.  Study results showed that all patients suffered treatment-related toxicities; common grade ≥3 toxicities were hypertension (17.1%), muscle weakness (17.1%), lymphopenia (14.6%), and hypophosphatemia (9.8%).  Researchers then compared the data with results from previous clinical trials assessing the clinical benefit of bevacizumab monotherapy.  They concluded that tandutinib with bevacizumab was as effective but more toxic than bevacizumab monotherapy.  Which of the following best describes this type of study?

A study is designed to describe the manifestations of coronavirus disease 2019 (COVID-19) on imaging studies, particularly on computerized tomography (CT) scans.  Eleven patients with COVID-19 are recruited for the study, and their CT findings are studied and characterized.  Which of the following best describes this study design?

The results of a study investigating a new diagnostic test for acute myocardial infarction (MI) are given in the table below. What is the sensitivity of the new diagnostic test?

Blood pressure measurements are obtained from a sample of individuals with no known medical conditions.  For systolic blood pressure (SBP), the mean measurements and associated standard deviations (SDs) are shown by age group for men and women: If hypertension is defined as SBP >140 mm Hg, approximately what percentage of men age 35-44 in this sample will be classified as having hypertension, assuming a normal (Gaussian) distribution?

Researchers develop a new test to detect the presence of a recently identified biomarker for hepatocellular carcinoma (HCC).  The initial evaluation of the test shows the following: Which of the following is the likelihood that a patient with a negative test does not have HCC?

A large, multi-country study is conducted to determine the effect of economic development on cancer incidence and mortality.  The study uses data obtained from the national cancer registries, along with information regarding per capita gross domestic product as reported by the International Monetary Fund and life expectancy as reported by the World Health Organization.  Which of the following best describes the design of this study?

The aim of a prospective cohort study conducted in a group of adults with diagnosed type 2 diabetes mellitus (T2DM) is to investigate the association between the presence of morbid obesity (BMI >40 kg/m²) and the risk of developing diabetic nephropathy.  One of the groups in the study consists of adults with T2DM, a BMI >40 kg/m², and no diabetic nephropathy.  Which of the following is the most appropriate comparison group for this prospective cohort study?

A research laboratory develops a new serologic test for detecting prostate cancer.  The new assay is compared to transrectal ultrasound-guided prostate biopsy to determine sensitivity and specificity parameters.  It is found that the test result is negative in 95% of patients who do not have the disease.  If the new assay is used on 8 blood samples taken from patients without prostate cancer, what is the probability of all 8 test results coming back negative?

A new study is conducted to investigate the efficacy of intravenous immunoglobulin versus analgesics on pain alleviation in patients with idiopathic small fiber neuropathy.  A total of 100 eligible patients who fulfilled the inclusion/exclusion criteria are assigned to one of two groups based on random selection by a computer.  The method of assigning patients to treatment groups in this study is most likely to produce which of the following?

A study is conducted to assess the effect of beta-blocker therapy in patients with acute myocardial infarction (MI).  The study found that 20 patients out of 90 who took a beta-blocker during the week prior to developing an MI had a major arrhythmia event during hospitalization.  The study also determined that 30 patients out of 70 who did not take any beta-blocker developed a major arrhythmia.  What was the odds ratio of developing major arrhythmia in patients who took beta-blockers compared to those who did not take beta-blockers?

A study is conducted to estimate the prevalence of catheter-associated urinary tract infection (CAUTI) in the intensive care unit (ICU) of an urban hospital.  The plot below shows the number of cases of CAUTI in this hospital during the month of July among patients in the ICU.  Based on the plot, which of the following is the number of prevalent cases on July 31?

A test is used to diagnose dementia in a population of 1,000 women age ≥75.  The test has a sensitivity of 80% and a specificity of 90%.  The test is then used as a diagnostic tool in 2 other populations of women of the same age: population 1 has a prevalence of dementia of 15%, and population 2 has a prevalence of dementia of 30%.  Which of the following best describes how the negative predictive values (NPV) and the positive predictive values (PPV) from populations 1 and 2 relate to each other?

Researchers at an academic trauma center conducted a randomized clinical trial comparing 2 surgical techniques (Technique A and Technique B) for repairing a mandible fracture.  They examined rates of infectious complications and rates of malocclusion (defined as misaligned dental arches on visual examination when the jaw is closed).  A total of 100 patients were enrolled in the study.  Outcome assessments of each patient were conducted at 2 weeks, 4 weeks, and 8 weeks after surgery.  Results showed that the relative rate of infection with Technique A compared with Technique B was 0.86 with a 95% confidence interval of 0.57-1.28; the 2 techniques had similar malocclusion rates at 8 weeks after surgery.  Which of the following statements most accurately represents the comparison of Technique A and Technique B in a clinical care setting?

A genome-wide association study (GWAS) of rheumatoid arthritis (RA) is performed in a cohort of Portuguese patients, including 907 cases with RA and 1,524 controls without RA.  Logistic regression is used to test the association between RA and hundreds of thousands of loci.  These association results are then compared with data from a European GWAS cohort of 4,036 patients with RA and 6,959 patients without RA.  Finally, the Portuguese and European study results are combined into a meta-analysis.  Based on these data, the investigators identify 3 new loci that are associated with RA based on a significance level threshold of 5 × 10⁻⁸: Previous studies had identified 30 loci that accounted for <35% of disease heritability for RA.  Which of the following statements is correct regarding this study?

A researcher studying physician behavior is interested in how often primary care physicians take the sexual histories of patients during clinic visits.  As part of the study, patients who attend a primary care clinic are asked to fill out a questionnaire immediately following a visit with their physician.  Once the physicians become aware that their own behavior is being studied, which of the following is most likely to be a potential problem?

A research group is studying the correlation between BMI and blood pressure in a random sample of children age 12-16.  After collecting data, they conduct a correlation analysis at a 1% significance level.  The researchers find that BMI correlates with systolic blood pressure with a coefficient of r = 0.46 (p <0.001) and diastolic blood pressure with a coefficient of r = 0.37 (p <0.001).  Which of the following is the most accurate interpretation of these results?