A study is conducted to describe the age-sex distribution of a certain country.  According to national data, the population pyramid of the country has the shape shown below.

Based on the population pyramid, which of the following is most likely true about this country and its population?

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 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?

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?

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?

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?

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?

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 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 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 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 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?

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?

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 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 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 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?

As part of the Food and Drug Administration drug approval process, a study is conducted to assess the clinical benefit and toxicity of a new drug that is intended to be used in combination with current standard chemotherapy for patients with recurrent glioblastoma.  Fifty patients with recurrent glioblastoma enroll in the trial and are randomized to receive standard chemotherapy plus either placebo or 1 of 3 possible doses of the new drug.  Study results show a dose-dependent reduction in tumor size with all 3 doses of the new drug, along with a significant increase in adverse drug effects, including hypertension, muscle weakness, lymphopenia, and hypophosphatemia.  The researchers conclude that the middle dose of the new drug offers the greatest ratio of benefit to toxicity.  Which of the following best describes this type of study?

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?

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 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?

 clinical study examines the usefulness of 5 different biomarkers to detect Barrett esophagus (BE), the only known precursor lesion of esophageal adenocarcinoma.  Researchers evaluate the performance of each biomarker and report the sensitivity, specificity, and area under the curve (AUC) estimates.

Which of the biomarkers is most accurate?

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 research group conducted a placebo-controlled clinical trial to assess whether a new drug to treat acute migraine with or without aura in adults is more effective than standard therapy.  A total of 3,500 patients with acute migraine were enrolled in the study and randomly assigned to either the new drug or standard treatment.  During the data analysis phase, the researchers decide to set alpha at 0.01 rather than 0.05.  Which of the following is the most likely result of this change?

The population pyramid of a certain country is shown below.

Based on the diagram, which of the following best characterizes this population?

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?

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 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?

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 surveillance study is conducted to assess the long-term efficacy and safety of a drug currently being used to treat patients with heart failure.  Researchers enroll 8,300 patients with heart failure.  The patients receive the drug once daily for 6 months.  The results show significant clinical improvement, but severe hypernatremia is observed in 23 patients.  The study publication recommends a lower dose of the drug in patients with baseline normonatremia and hypokalemia to prevent hypernatremia.  Which of the following best characterizes this type of study?

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 group of sports physicians plans to conduct a case-control study to investigate a possible association between adolescent idiopathic scoliosis (AIS) and sacroiliac joint (SIJ) dysfunction in young athletes.  The case group will consist of young athletes who were diagnosed with AIS during a regular checkup by a sports physician.  Which of the following is the most appropriate control group for this study?

The specificity of the standard test to detect disease X in the general population is 73%.  A team of researchers set forth a goal to increase specificity for detecting disease X.  They develop a new test and conduct a study to evaluate its performance on a random sample from the general population.  The results of their study are shown below.

According to these results, have the researchers achieved their goal?

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?

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 pediatric cardiologist decides to determine whether there is a relationship between body composition and blood pressure in a random sample of children and adolescents age 5-15.  He used standard procedures to collect anthropometric measurements that included weight, height, hip circumference (HC), and waist circumference (WC).  Systolic blood pressure (SBP) and diastolic pressure (DBP) readings were taken at least 3 times at 5-minute intervals after the participants had been seated, and average SBP and DBP readings were calculated based on these measurements.  Which of the following statistical tests is adequate to determine whether there is a relationship between WC and average DBP?