Exam 4: Biostatistics

Researchers are studying the relationship between essential hypertension and a common mutation in the structure of a sodium channel protein.  A study population is randomly selected and blood samples are obtained for leukocyte genotyping.  The prevalence of hypertension is determined based on mean blood pressure measurements obtained using standardized ambulatory blood pressure monitoring conducted over 1 week.  Based on the analysis results, the researchers conclude that the sodium channel structure mutation is associated with hypertension.  Which of the following best describes the study design used by the investigators?

A study is performed to compare the effect of tramadol when compared to placebo for painful polyneuropathy.  Fifty patients are selected and randomly allocated to 1 of 2 treatment sequences:  Tramadol followed by placebo, or placebo followed by tramadol.  The initial treatment period is delivered for 4 weeks followed by an interim 1-week washout phase, after which the second treatment period is delivered for an additional 4 weeks.  After each treatment period, patients use a 10-point numeric scale to rate pain, paresthesia, and tenderness.  Which of the following best describes this study design?

An investigator is conducting a randomized, double-blind, placebo-controlled clinical trial of a new drug for the treatment of peripheral neuropathy in adults with multiple myeloma (MM).  One hundred fifty patients with MM are enrolled in the trial and randomized to receive either the new drug (n = 75) or placebo (n = 75).  Trial protocol requires that patients in both groups take 1 pill per day and keep a pain diary.  After 3 months of treatment, each patient is interviewed, and the pain diaries are reviewed; 9 patients taking the new drug and 3 patients taking placebo did not take the pills as instructed.  The investigator decides to conduct an intention-to-treat analysis of the study data.  Which of the following best describes how the data pertaining to all patients who did not adhere to protocol should be treated?

A surveillance study is conducted to assess the efficacy and safety of tolvaptan, a drug currently being used in the clinical setting for treating heart failure with volume overload.  The study enrolls 8,300 patients with a variety of medical comorbidities who received tolvaptan once daily in the morning for 2 weeks.  Results showed that tolvaptan demonstrated aquaretic efficacy in patients with diuretic-resistant volume overload, but that hypernatremia was a complication in a small number of patients.  Researchers recommended a lower dose of tolvaptan in those with normonatremia and hypokalemia to prevent hypernatremia.  Which of the following best describes this type of study?

A research group conducted a study to compare the levels of creatine kinase-MB (CK-MB) between type 2 diabetes mellitus (T2DM) patients given statin therapy.  Participants were divided into 4 groups based on treatment.  Groups I, II, and III consisted of T2DM patients who had been given statin therapy (atorvastatin, simvastatin, rosuvastatin, respectively) for at least 6 months.  Group IV consisted of T2DM patients who had not been given statin therapy.  Which of the following statistical tests is most appropriate to compare the CK-MB levels between Groups I, II, III, and IV in this study?

Results of a recent study on the association between levels of glycosylated hemoglobin (HbA1c) and levels of high-sensitivity C-reactive protein (hs-CRP) in patients with type II diabetes mellitus (T2DM) read as follows:"The results of our study show that levels of HbA1c positively correlated with the levels of hs-CRP (r = 0.80).  The probability that these results were due to chance alone is 3%, with a 10% chance of concluding no relationship between HbA1c and hs-CRP when one truly exists."Based on this information, which of the following most likely represents the p-value and the power of the correlation test in the study?

A medical student is conducting a chart review of patients admitted to the local emergency department with acute pancreatitis.  He is interested in comparing blood glucose levels between mild and severe cases.  Before attempting to compare the mean blood glucose levels between the 2 groups of patients, he decides to conduct a descriptive analysis of the variables in each group.  Blood glucose levels in patients with severe acute pancreatitis were found to have a strong positively skewed distribution.  Which of the following is most likely to be true regarding the data for the severe acute pancreatitis group?

A study is conducted to assess the effectiveness of a new medication X added to standard antihypertensive therapy compared to standard antihypertensive therapy alone for preventing the development of proteinuria in patients recently diagnosed with essential hypertension.  Five years after diagnosis, 97 of 100 patients on the medication X + standard antihypertensive therapy regimen have not developed proteinuria, and 90 of 100 patients on a standard antihypertensive therapy regimen have not developed proteinuria.  According to these results, which of the following represents the approximate number of patients with essential hypertension who need to be treated with medication X to prevent an additional patient from developing proteinuria within 5 years?

Researchers are developing an enzyme-linked immunosorbent assay test for diagnosing rheumatoid arthritis.  The test is designed to detect the presence of serum antibodies against citrullinated proteins.  Two test populations with a differing prevalence of rheumatoid arthritis are selected.  The researchers plan to assess the test's performance in the 2 populations by comparing a number of diagnostic test parameters.  Which of the following performance measures is most likely to be different between the 2 test populations?

A group of researchers wants to identify factors related to hospital-acquired bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA).  A total of 45 patients were enrolled in the study after MRSA was isolated from a blood sample taken from them on the third or subsequent day after admission.  In addition, 90 patients admitted to the hospital over the same period with a length of stay >2 days who did not have bacteremia were randomly selected.  The frequency of factors such as insertion of a central line or urinary catheter and surgical site infection were then compared between the 2 groups.  Which of the following is the most appropriate null hypothesis for this study?

A new tumor marker is being investigated for its usefulness in diagnosing ovarian cancer.  A sample of 400 women is stratified into 2 groups based on the presence or absence of BRCA mutations.  Serum levels of the new marker are obtained in the 2 groups; in addition, both groups of women undergo conventional screening to determine their disease status.  The curves on the top represent the distribution of the new serum marker in women with BRCA mutations, and the curves on the bottom represent the distribution of the new serum marker in women without the BRCA mutations. The proposed serum marker cutoff value for both populations is shown.  Use of the new serum marker in women with BRCA mutations, compared with those without BRCA mutations, is associated with which of the following?

The prevalence of a chronic disease that affects mostly older individuals has been constant in a population for the last 15 years.  As a result of worsening economic conditions that have no effect on the disease itself, many young healthy individuals emigrate from the population.  Which of the following is the most likely effect of the emigration on the estimate of disease prevalence over the next few years?

A sample of children age 2-5 years is chosen at random from an outpatient clinic.  The number of urinary tract infections (UTIs) over a 1-year period is given in the figure below. What was the average number of UTI episodes over 1 year for a child in this sample?

A new biomarker has been shown to allow for the early detection of non-small cell lung carcinoma.  A preliminary analysis on a cohort study of this new test demonstrates that its use prolongs survival of lung cancer patients by 3 months when compared to the survival of patients diagnosed by conventional methods.  A secondary analysis reveals no difference in 6-month mortality rates between the 2 groups.  Which of the following factors most likely explains the study results?

A study compared drug A versus standard therapy in preventing recurrent pulmonary embolism (PE).  The absolute risk reduction for drug A versus standard therapy was 4%.  The incidence of recurrent PE in the standard therapy group was 6%.  There were 24 patients who developed recurrent PE in the drug A group.  How many total subjects were there in the drug A group?

Inflammatory biological markers are clinically useful in a number of different ways, one being the assessment of disease activity in conditions such as systemic lupus erythematosus (SLE).  A new inflammatory marker is being investigated in patients with active SLE flares.  When the blood level of the new marker (in mg/L) is plotted against the C-reactive protein (CRP) level (also in mg/L), the following plot is obtained: Based on the plot, the correlation coefficient between the 2 variables is closest to which of the following values?

A large study of serum folate levels in a sample of women age 16-45 reveals that this parameter is normally distributed with a mean of 5.0 ng/mL and a standard deviation of 0.5 ng/mL.  According to the study results, 95% of serum folate observations in these patients will lie approximately between which of the following limits?

A study was conducted to assess the age at menarche among young female gymnasts.  Based on commitment to the sport, gymnasts were divided into two groups: competitive gymnasts and recreational gymnasts. Assuming that age at menarche is normally distributed, which of the following is closest to the probability that a randomly chosen competitive gymnast will have onset of menarche at age ≥16?

A randomized controlled trial is conducted to compare transcatheter aortic valve replacement (TAVR), using a self-expanding transcatheter aortic valve bioprosthesis, with surgical aortic valve replacement in patients with severe aortic stenosis.  The objective is to determine the difference in risk of death from any cause.  Seven hundred forty-seven patients with severe aortic stenosis who are at increased surgical risk are recruited and randomly assigned to groups for treatment with TAVR or surgical valve replacement.  Follow-up assessments are performed at discharge and at 1 month, 6 months, and 1 year.  The 1-year follow-up results are as follows: Which of the following best represents the absolute risk reduction for death from any cause in patients treated with TAVR compared to those treated with surgical replacement?

In a reference sample of hundreds of healthy subjects, the laboratory reference range for a novel marker of cardiac injury is 0.04-0.08 U/mL at the standard 95% level of probability.  The marker has very high sensitivity and specificity for myocardial tissue.  The clinical cardiology team would like to use a 99.7% reference range to assess patients who come to the emergency department with chest pain and have a high pretest probability of cardiac ischemia.  An elevated value of the marker is defined as exceeding the 99.7th percentile of the reference sample.  Assuming a normal (Gaussian) distribution with a mean of 0.06 U/mL, which of the following most closely approximates the corresponding reference range?