Exam 4: Biostatistics

A case-control study was conducted to estimate the association between simvastatin therapy and serum levels of fibrinogen in patients who underwent percutaneous coronary intervention.  Cases were identified as patients who underwent percutaneous coronary intervention and had high periprocedural levels of fibrinogen (>400 mg/dL), and controls were identified as patients who underwent percutaneous coronary interventions but had normal levels of fibrinogen (200-400 mg/dL).  History of simvastatin therapy use was assessed through chart review for every patient.  The number of patients corresponding to each classification criteria is given in the table below. Which of the following is the best statistical method to estimate the association between simvastatin use and high serum fibrinogen levels in this study?

A 54-year-old man with hypertension and hyperlipidemia who came to the emergency department with chest pain wants to know if he is having a heart attack.  Test A is newly available for diagnosing myocardial infarction (MI).  In a recent study, the results of test A (compared to a gold standard diagnosis of MI) were as follows: The patient has a positive result on test A.  Assuming his pre-test probability is equivalent to the prevalence of MI in the study, what is the probability that the patient has an MI?

A 62-year-old man with diabetes, hypertension, and hyperlipidemia comes to the emergency department of an academic medical center with chest pain, nausea, vomiting, and diaphoresis.  An electrocardiogram demonstrates ST elevation in the anterior leads, and cardiac enzymes are markedly elevated.  Investigators at the center are designing a randomized control trial to test the hypothesis that drug B will decrease the mortality associated with acute ST-elevation myocardial infarction compared to standard of care.  To ensure that investigators will not miss a difference between drug B and standard of care (if a difference truly exists), which of the following would they want to maximize?

A study examined the effect of a low-carbohydrate diet compared to a low-fat diet on body weight.  A sample of 150 overweight but otherwise healthy adults from a large city was enrolled in the study and randomly assigned in a 1:1 ratio to either the low-carbohydrate (40 g/d) or the low-fat (<7% saturated fat) diet.  At 12 months, a greater body weight change was reported in the low-carbohydrate diet group compared to the low-fat diet group, with a mean difference in body weight change of −3.5 kg (p = 0.01, predetermined significance level = 0.05).  Which of the following is the most accurate interpretation of the results of this study?

A study determines that the mean blood cholesterol level is 195 mg/dL in 200 non-diabetic hospitalized patients and 210 mg/dL in 180 diabetic hospitalized patients.  The probability that the observed difference is due to chance alone is reported to be 5%.  There is also a 20% probability of concluding that there is no difference in blood cholesterol level when there is one in reality.  What is the power of the study?

A study evaluated the role of angiotensin-converting enzyme (ACE) inhibitors in the prevention of coronary events in patients with diabetes.  During 5 years of follow-up, 120 out of 400 diabetic patients who had taken an ACE inhibitor developed an acute coronary event.  Over the same time, 100 out of 300 diabetic patients who had not taken an ACE inhibitor experienced coronary events.  What was the relative risk of developing a coronary event in diabetic patients who were taking ACE inhibitors compared to diabetic patients who were not taking ACE inhibitors?

A geneticist is interested in the potential causes of a congenital abnormality.  She hypothesizes that acetaminophen use during the first trimester of pregnancy might be associated with the abnormality.  In her study, a sample of mothers of children with and without the abnormality are randomly selected from government birth records.  Personal interviews are then conducted with the mothers to determine fetal exposure to acetaminophen.  Results show that mothers of children who do not have the abnormality did not take acetaminophen as frequently during the first trimester.  This type of study is most susceptible to which of the following types of bias?

A community health task force is preparing to launch a campaign promoting obesity awareness and education in the area.  The task force studies epidemiologic data from the county health department, which show that the prevalence of obesity is 3 times higher in a cluster of 5 specific ZIP codes compared to the county average.  The task force leader approaches a reputed physician working at a local university to ask for assistance in understanding this pattern.  Which of the following should be performed first to understand the etiology of the disparity in obesity prevalence?

The graph below shows the yearly incidence of viral hepatitis per 100,000 population from 1982-2012 in the United States (US). During this period, the total population in the US continued to increase, as shown in the table below: At any given time point, the number of individuals at risk for hepatitis infection is assumed to be equal to the total US population.  Based on these data, which of the following is most likely to be true?

A state's population for 2016 was estimated at 4,000,000.  At the beginning of the same year, the state reported having 20,000 cases of a rare and fatal neurodegenerative condition.  At the end of 2016, the state reported 7,000 new cases, as well as 1,000 deaths attributable to this condition.  Another 40,000 deaths from all other causes were also reported at the end of the year.  What was the cumulative incidence of the disease in 2016?

A large prospective study evaluates the relationship between alcohol consumption and breast cancer.  A total of 4000 middle-aged women are enrolled in the study through a random selection of residential addresses.  Daily alcohol consumption and breast cancer incidence are assessed through the use of periodic questionnaires.  On five-year follow-up, the investigators report the association between alcohol consumption and breast cancer as a relative risk of 1.32 (95% confidence interval = 0.90-1.85); 800 subjects were lost to follow-up by the end of the study, the majority of whom were moderate to heavy alcohol consumers.  According to this information, which of the following biases is most likely to be present and may have affected the results?

Researchers want to explore the association between selective serotonin reuptake inhibitor (SSRI) use and pulmonary tuberculosis.  A random sample of subjects age 20-84 with newly diagnosed pulmonary tuberculosis and an independent random sample of subjects without pulmonary tuberculosis are enrolled in the study.  Subsequently, subjects who never had a prescription for an SSRI are defined as "never users," and those who have had a prescription for an SSRI are defined as "users."  The study compares the frequency of SSRI use in subjects with and without a diagnosis of pulmonary tuberculosis and determines that SSRI use is not associated with pulmonary tuberculosis.  Which of the following best describes the design of this study?

Carbamoyl phosphate synthetase I deficiency is an inherited disorder characterized by accumulation of ammonia in the blood.  The most severe form occurs in the first 24-72 hours following birth, after feeding begins and milk proteins start to be broken down in the liver.  If left untreated, affected neonates often die due to severe metabolic derangements; survivors often develop permanent neurologic injury.  The estimated incidence of carbamoyl phosphate synthetase I deficiency is about 1 in 800,000 newborns.  If a decision is made to test all newborns for this disease, then this initial test should be designed to have a high:

A physician research group is evaluating the efficacy of a new lipid-lowering drug, Superstatin, which is being marketed directly to consumers as a groundbreaking new therapy to prevent heart attacks.  The drug manufacturer claims that the drug is more effective than existing hypolipidemic agents for primary prevention of myocardial infarction.  Results of a 5-year, randomized, double-blinded, controlled study to evaluate the efficacy of Superstatin are shown below. Compared to the control medication, how many patients need to be treated with Superstatin to prevent one additional myocardial infarction?

A 65-year-old man comes to the office because his family is concerned about his constant cough after smoking.  The patient asks about the risk of developing chronic obstructive pulmonary disease (COPD) in adult smokers.  A recent cohort study reported that compared to heavy smokers, the relative risk (RR) of COPD for nonsmokers is 0.10 and for moderate smokers is 0.40.  The patient is a moderate smoker.  Based on the study, which of the following is the RR of COPD for moderate smokers compared to nonsmokers?

A study aims to investigate the effectiveness of the topical application of tetracycline ointment in the prevention of surgical-site infection associated with resection of advanced oral cavity cancer.  Fifty patients who underwent locoregional resection were assigned by chance to receive standard care alone or tetracycline-ointment in addition to standard care.  The patients were then followed for 1 month and the number and severity of surgical-site infections were recorded for each group.  Which of the following best describes the study design?

A new estrogen receptor agonist is being evaluated for the treatment of postmenopausal symptoms.  A prospective study shows that the drug increases the risk of deep vein thrombosis (DVT) in treated women who smoke compared to untreated women who smoke, with a relative risk (RR) of 1.70 and p-value of 0.01.  In nonsmokers, no increased risk of DVT is evident with use of the drug (RR = 0.96; p-value = 0.68).  Which of the following describes this phenomenon?

A physician is conducting a double-blind randomized controlled trial to determine the effect of a new cream in reducing the risk of relapse in chronic recurrent atopic dermatitis.  A total of 30 patients with moderate to severe atopic dermatitis who were experiencing a flare are randomly divided into 2 groups: 15 patients will receive the new cream, and 15 patients will receive emollient alone.  The rate of relapse after 2 weeks of treatment is 25% in the group who received the new cream and 50% in the group who received emollient alone.  However, the difference is found to be not statistically significant (p = 0.14).  The physician concludes that use of the new cream does not reduce the risk of relapse in chronic recurrent atopic dermatitis.  Which of the following is most likely to explain the results of the study?

A group of researchers conduct a study to evaluate the pharmacologic properties of oxfendazole, an anthelminthic agent.  As part of the study, increasing oral doses of oxfendazole (0.5 to 60 mg/kg) are administered to healthy volunteers.  Data is collected to form a pharmacokinetic profile of the drug and its metabolites, and the incidence of adverse effects is recorded for the various dosages.  A total of 20 healthy male and female (nonchildbearing potential) volunteers participate in the study.  Oxfendazole is found to be well tolerated throughout the dose range without any serious adverse effects or deaths.  Which of the following best describes this type of study?

The population pyramid of a certain country is shown below. Based on the diagram, which of the following best characterizes this population?