Biostatistics Book Review

• A new combined chemotherapy and immunotherapy regimen has been shown to significantly prolong survival in patients with metastatic melanoma. If widely implemented, which of the following changes in disease occurrence measures would you most expect? >>A)
• (Correct) Incidence does not change, prevalence increases
• Incidence increases, prevalence decreases
• Incidence decreases, prevalence decreases
• Incidence increases, prevalence increases
• Incidence does not changes, prevalence does not change
• The incidence of diabetes mellitus in a population with very little migration has remained stable over the past 40 years ($\pu{55 cases}$ per $\pu{1000 people}$ per year). At the same time, prevalence of the disease increased threefold over the same period. Which of the following is the best explanation for the changes in diabetes occurrence measures in the population? >>A)
• (Correct) Improved quality of care
• Increased diagnostic accuracy
• Poor event ascertainment
• Increased overall morbidity
• Loss at follow-up
• In a survey of $\pu{10,000}$ IV drug abusers in town A, $\pu{1,000}$ turn out to be infected with hepatitis C and $\pu{500}$ infected with hepatitis B. During two years of follow-up, $\pu{200}$ patients with hepatitis C infection and $\pu{100}$ patients with hepatitis B infection die. Also during follow-up, $\pu{200}$ IV drug abusers acquire hepatitis C and $\pu{50}$ acquire hepatitis B. Which of the following is the best estimate of the annual incidence of hepatitis C infection in IV drug abusers in town A? >>A)
• (Correct) 100/9,000
• 1,000/10,000
• 1,100/10,000
• 100/10,000
• 100/9,800
• If data shows a significant increase in the vaccination rate for hepatitis B among IV drug abusers in a specific town, which of the following hepatitis D statistics is most likely to be affected by this reported data? >>A)
• (Correct) Incidence
• Hospitalization rate
• Case fatality rate
• Median survival
• Cure rate
• In a city having a population of $\pu{1,000,000}$ there are $\pu{300,000}$ women of childbearing age. The following statistics are reported for the city in the year 2000:
• Fetal deaths: $\pu{200}$
• Live births: $\pu{5,000}$
• Maternal deaths: $\pu{70}$

Which of the following is the best estimate of the maternal mortality rate in the city in the year 2000? >>A) - (Correct) 70/5,000 - 70/1,000,000 - 70/300,000 - 70/5,200 - An observational study in diabetics assesses the role of an increased plasma fibrinogen level on the risk of cardiac events. $\pu{130}$ diabetic patients are followed for $\pu{5 years}$ to assess for the development of acute coronary syndrome. In a group of $\pu{60}$ patients with a normal baseline plasma fibrinogen level, $\pu{20}$ develop acute coronary syndrome and $\pu{40}$ do not. In a group of $\pu{70}$ patients with a high baseline plasma fibrinogen level, $\pu{40}$ develop acute coronary syndrome and $\pu{30}$ do not.

Which of the following is the best estimate of relative risk in patients with a high baseline plasma fibrinogen level compared to patients with a normal baseline plasma fibrinogen level? >>A) - (Correct) (40/70)/(20/60) - (40/30)/(20/40) - (4040)/(2030) - (4070)/(2060) - (40/60)/(20/70) - A study is performed in which mothers of babies born with neural tube defects are questioned about their acetaminophen consumption during the first trimester of pregnancy. At the same time, mothers of babies born without neural tube defect are also questioned about their consumption of acetaminophen during the first trimester. Which of the following measures of association is most likely to be reported by investigators? >>A) - (Correct) Odds ratio - Prevalence ratio - Median survival - Relative risk - Hazard ratio - At a specific hospital, patients diagnosed with pancreatic carcinoma are asked about their current smoking status. At the same hospital, patients without pancreatic carcinoma are also asked about their current smoking status. The following table is constructed:

What is the odds ratio that a patient diagnosed with pancreatic cancer is a current smoker compared to a patient without pancreatic cancer? >>A) - (Correct) (50/40)/(60/80) - (50/90)/(60/140) - (50/110)/(40/120) - (50/60)/(40/80) - (90/230)/(140/230) - Which type of scatter plot graph most closely corresponds to a correlation coefficient of $+1.0$? >>A) - (Correct) A graph where all data points fall exactly on a straight line with a positive slope - A graph with a horizontal line of data points - A graph with a vertical line of data points - A graph where all data points fall exactly on a straight line with a negative slope - A graph with scattered points showing a general upward trend but not a perfect line - A group of investigators describes a linear association between calcium content of the aortic valve cusps as measured in vivo and the diameter of the aortic opening. They report a correlation coefficient of $-0.45$ and a $p$ value of $0.001$. Which of the following is the best interpretation of the results reported by the investigators? >>A) - (Correct) As calcium content of the cusps increases the aortic valve diameter decreases - Alpha-error level is set too low - Sample size is too low for drawing definite conclusions - Calcium deposition causes narrowing of the aortic valve opening - As aortic valve diameter decreases the calcium content of the cusps decreases - A study is conducted to assess the relationship between plasma homocysteine level and folic acid intake. The investigators demonstrate that the plasma homocysteine level is inversely related to folic acid intake, and the correlation coefficient is $-0.8$ ($p < 0.01$). According to the information provided, how much of the variability in plasma homocysteine levels is explained by folic acid intake? >>A) - (Correct) 0.64 - > 0.99 - 0.80 - 0.55 - < 0.01 - In a small observational study, $\pu{100 industrial workers}$ are followed for $\pu{1 year}$ to assess for the development of respiratory symptoms (defined as productive cough lasting at least one week). $\pu{30 of 60 smokers}$ experience respiratory symptoms over the year versus $\pu{10 of 40 non-smokers}$. Which of the following is the best estimate of the attributable risk of respiratory disease in smokers? >>A) - (Correct) 0.25 - 0.75 - 0.50 - 0.30 - 0.10 - In a small observational study, $\pu{100 industrial workers}$ are followed for $\pu{1 year}$ to assess for the development of respiratory symptoms (defined as productive cough lasting at least one week). $\pu{30 of 60 smokers}$ experience respiratory symptoms over the year versus $\pu{10 of 40 non-smokers}$. What percentage of respiratory disease experienced by smokers is attributed to smoking? >>A) - (Correct) 50% - 90% - 75% - 25% - 10% - In a small observational study, $\pu{100 industrial workers}$ are followed for $\pu{1 year}$ to assess for the development of respiratory symptoms (defined as productive cough lasting at least one week). $\pu{30 of 60 smokers}$ experience respiratory symptoms over the year versus $\pu{10 of 40 non-smokers}$. What percentage of respiratory disease experienced by all study subjects is attributed to smoking? >>A) - (Correct) 20% - 75% - 50% - 25% - 10% - A new chemotherapy regimen used in patients with ovarian carcinoma is tested in a small clinical trial. Out of $\pu{50 patients}$ treated with the new regimen, $\pu{25 survive}$ $\pu{5 years}$ without relapse. Out of $\pu{100 patients}$ treated with the conventional regimen, $\pu{25 survive}$ $\pu{5 years}$ without relapse. How many patients need to be treated with the new regimen as opposed to the conventional regimen in order for one more patient to survive $\pu{5 years}$ without relapse? >>A) - (Correct) 4 - 2 - 6 - 8 - 10 - A group of investigators conducts a study to evaluate the association between serum homocysteine level and the risk of myocardial infarction. They conclude that a high baseline plasma homocysteine level is associated with an increased risk of myocardial infarction and report a risk ratio (RR) of $1.08$ and a $p$ value of $0.01$. Which of the following is the most accurate statement about the results of the study? >>A) - (Correct) There is a 1% probability that there is no association - There is an 8% chance that increased homocysteine levels cause myocardial infarction - The 95% confidence interval for the RR includes 1.0 - The study has insufficient power to reach a definite conclusion - There is a 10% probability that the association is underestimated - High plasma C-reactive protein (CRP) level is believed to be associated with increased risk of acute coronary syndromes. A group of investigators is planning a study that would evaluate that association, taking into account a set of potential confounders. Which of the following is the best statement of null hypothesis for the study? >>A) - (Correct) High plasma CRP level has no association with acute coronary syndrome - High plasma CRP level carries increased risk of acute coronary syndromes - High plasma CRP level is related to the occurrence of acute coronary syndromes - Acute coronary syndrome can be predicted by high plasma CRP - High plasma CRP level can cause acute coronary syndromes - Two studies are conducted to assess the risk of developing asymptomatic liver mass in women taking oral contraceptive pills (OCP). Study A reports a relative risk of $1.6$ (95% confidence interval $1.1-2.8$) in women taking OCP compared to women not taking OCP over a $\pu{5-year}$ follow-up period. Study B reports a relative risk of $1.5$ (95% confidence interval $0.8-3.5$) in women taking OCP compared to women not taking OCP over a $\pu{5-year}$ follow-up period. Which of the following statements about the two studies is most accurate? >>A) - (Correct) The sample size in study B is small - Study A overestimates the risk - The result in study B proves no causality - The result in study A is not accurate - The p value in study B is less than 0.05 - A ten-year prospective study is conducted to assess the effect of regular supplementary folic acid consumption on the risk of developing Alzheimer’s dementia. The investigators report a relative risk of $0.77$ (95% confidence interval $0.59 - 0.98$) in those who consume folic acid supplements compared to those who do not. Which of the following $p$ values most likely corresponds to the results reported by the investigators? >>A) - (Correct) 0.03 - 0.05 - 0.07 - 0.09 - 0.15 - A double-blind clinical study is conducted in patients with chronic heart failure, class II and III, treated with an ACE inhibitor and a loop diuretic. One group receives metoprolol and the other group receives placebo. The following relative risk values are reported for the metoprolol group compared to the placebo group:

Which of the following provides the best interpretation for the obtained results? >>A) - (Correct) Beta-blockers protect from myocardial infarction but do not affect the risk of stroke - Beta-blockers decrease both all-cause mortality and cardiovascular mortality - Beta-blockers predispose to a stroke - Beta-blockers affect all-cause mortality due to decreased risk of myocardial infarction - Beta-blockers may exacerbate heart failure but they decrease cardiovascular mortality - In an experimental study, patients suffering from stable angina are treated with a new beta-blocker. The number of anginal episodes experienced by the patients on the thirtieth day of treatment is shown below: * $\pu{50 patients}$: $\pu{0 episodes}$ * $\pu{30 patients}$: $\pu{1 episode}$ * $\pu{10 patients}$: $\pu{2 episodes}$ * $\pu{10 patients}$: $\pu{3 episodes}$

Based on these data, what is the average number of anginal episodes experienced by patients treated with the new drug? >>A) - (Correct) Between 0 and 1 - 1 - Between 1 and 2 - 2 - Between 2 and 3 - An ICU patient has an intraarterial canula placed after cardiac surgery to monitor systolic blood pressure (SBP). Twenty-four SBP values are recorded over a period of $\pu{6 hours}$, with a maximum value of $\pu{141 mmHg}$ and a minimum value of $\pu{96 mmHg}$. If the next SBP recording is $\pu{200 mmHg}$, which of the following is most likely to remain unchanged? >>A) - (Correct) Mode - Mean - Range - Variance - Standard deviation - A patient with severe heart failure is placed in the ICU and undergoes invasive hemodynamic monitoring. Over the next hour, the recorded values of his pulmonary artery wedge pressure are $\pu{26 mmHg}$, $\pu{20 mmHg}$, $\pu{20 mmHg}$, $\pu{27 mmHg}$, $\pu{14 mmHg}$ and $\pu{27 mmHg}$. Which of the following is the median of the recorded values? >>A) - (Correct) 23 - 20 - 24 - 26 - 27 - Four separate studies assess the risk of acute coronary syndrome in post-menopausal women taking hormone replacement therapy. Each study result is presented as an odds ratio along with a confidence interval. A meta-analysis is then performed combining these results. Which characteristic would most likely distinguish the meta-analysis result from the individual studies? >>A) - (Correct) A narrower confidence interval - A much higher odds ratio - A much lower odds ratio - A wider confidence interval - A confidence interval that always includes 1.0 - A study addresses the role of air pollution in asthma development. $\pu{100 children}$ with diagnosed asthma and $\pu{200 children}$ without asthma are asked about their homes. The mean air pollution index for children with asthma is $\pu{4.3}$ (95% confidence interval $3.1 — 5.5$). Which of the following statistical changes would be most likely if more asthmatic children were included in the study? >>A) - (Correct) Standard error of the mean decreases, narrowing the confidence interval - Standard error of the mean increases - Upper confidence limit increases - Lower confidence limit decreases - No change in the confidence interval width - In a graphical distribution of serum marker levels for healthy and diseased populations, if the overlap between the two curves decreases (the curves become “taller and narrower” or move further apart), this change is associated with: >>A) - (Correct) Higher sensitivity and higher specificity - Higher sensitivity and lower specificity - Higher sensitivity and same specificity - Lower sensitivity and higher specificity - Lower sensitivity and lower specificity - A new diagnostic test for tuberculosis has a sensitivity of 90% and a specificity of 95%. If applied to a population of $\pu{100,000 patients}$ in which the prevalence of tuberculosis is 1%, how many false negative results would you expect? >>A) - (Correct) 100 - 10 - 50 - 500 - 900 - 1,000 - 9,000 - A rare disorder of amino acid metabolism causes severe mental retardation if left untreated. If the disease is detected soon after birth a restrictive diet prevents mental abnormalities. Which of the following characteristics would be most desirable in a screening test for this disease? >>A) - (Correct) High Sensitivity - High Specificity - High Positive predictive value - High Cutoff value - High Accuracy - A rapid test that is used to diagnose HSV infection is positive in HSV-infected patients 9 times more often than in non-infected patients. Which of the following expressions is used to derive this information? >>A) - (Correct) Sensitivity/(1 - Specificity) - True positives/All positives - True positives/True negatives - Sensitivity/Specificity - Specificity/(1 — Sensitivity) - A new serum marker is tested as a fetal antigen for colon cancer. Sensitivity and specificity are plotted on a receiver operating characteristic (ROC) curve at various cutoff points (P1, P2, and P3). P3 is located higher and further to the right on the curve than P1 (P3 has higher sensitivity but lower specificity than P1). Which of the following is the best statement concerning this new test? >>A) - (Correct) P3 corresponds to a lower serum marker value than does P1 - P1 represents the cutoff point with the best ‘ruling out’ possibility - P2 represents the cutoff point with the best ‘ruling in’ possibility - P3 corresponds to the cutoff point with the highest positive predictive value - The higher the serum marker level used as a cutoff point, the lower the specificity - A $\pu{38-year-old}$ Caucasian primigravida is concerned about the risk of Down syndrome. You explain that triple screening may detect up to 50% of cases and amniocentesis may detect up to 90%. While comparing both tests during patient counseling, the difference in “up to 50%” vs “up to 90%” specifically refers to differences in: >>A) - (Correct) Sensitivity - False negatives - False positives - Positive predictive value - Negative predictive value - A new stool test for $\ce{H. pylori}$ infection yields positive results in 80% of infected patients and in 10% of uninfected patients. Prevalence of $\ce{H. pylori}$ infection in the population is 10%. What is the probability that a patient who tests positive with the new test is infected with $\ce{H. pylori}$? >>A) - (Correct) 47% - 25% - 33% - 54% - 75% - A $\pu{52-year-old}$ Caucasian female presents with a self-palpated thyroid nodule. Fine-needle aspiration (FNA) of the nodule is performed and the result is negative. You tell the patient the probability of thyroid cancer is low because FNA has a high: >>A) - (Correct) Negative predictive value - Specificity - Sensitivity - Positive predictive value - Validity - A serologic test for hepatitis C virus (HCV) infection has sensitivity and specificity of 85% and 78%, respectively. If the test is applied to a population of IV drug abusers (who have a higher probability of HCV infection than the general population), which of the following changes in test performance parameters would you expect? >>A) - (Correct) Specificity no change, PPV increases, NPV decreases - Specificity increases, PPV increases, NPV decreases - Specificity no change, PPV increases, NPV increases - Specificity decreases, PPV decreases, NPV increases - Specificity decreases, PPV decreases, NPV decreases - In a distribution of serum marker levels where the “Healthy” curve is to the left and “Diseased” curve is to the right, if the cutoff point is moved from a higher value (X) to a lower value (A) such that sensitivity increases, the positive predictive value will: >>A) - (Correct) Decrease - Increase - Remain unchanged - Cannot be determined based on the data provided - $\pu{190 patients}$ with exercise-induced chest pain undergo stress ECG followed by coronary angiography. Coronary angiography is positive if luminal stenosis is $\ge 70\%$. Results: * Stress ECG Positive, Angiography Positive: $\pu{90}$ * Stress ECG Positive, Angiography Negative: $\pu{10}$ * Stress ECG Negative, Angiography Positive: $\pu{12}$ * Stress ECG Negative, Angiography Negative: $\pu{78}$

If a patient has a negative ECG stress test, what is his/her probability of having a positive result on coronary angiography? >>A) - (Correct) 13% - 10% - 11% - 12% - 15% - Several tests have been developed to measure serologic markers of breast cancer. If positive, which of the following tests will have the highest predictive value for the disease? >>A) - (Correct) Sensitivity 65%, specificity 97% - Sensitivity 80%, specificity 90% - Sensitivity 70%, specificity 94% - Sensitivity 75%, specificity 92% - Sensitivity 85%, specificity 90% - A new screening test for stomach cancer increases survival by several weeks compared to endoscopic evaluation. This increase is statistically significant, although no difference is detected in the rate of radical gastrectomy between the two groups. Which of the following is most likely to affect the study results presented above? >>A) - (Correct) Lead-time bias - Low sensitivity - Selection bias - Confounding - Recall bias - A new screening test for prostate cancer tends to diagnose non-aggressive forms of the disease but often misses more aggressive forms. An apparent increase in survival after implementation of the test would be most likely affected by: >>A) - (Correct) Length-time bias - Confounding - Selection bias - Ascertainment bias - Measurement bias - An investigator suspects that acetaminophen use during the first trimester of pregnancy can cause neural tube defects. He estimates the general population risk of having neural tube defect is $1:1,000$. Which of following is the best study design to investigate the hypothesis? >>A) - (Correct) Case Control Study - Cohort Study - Clinical Trial - Ecologic Study - Cross-Sectional Study - Investigators study the relationship between a particular 5-lipoxygenase genotype and atherosclerosis. A study population is randomly selected. Blood samples are obtained for genotype, and ultrasonography is performed to assess carotid intima-media thickness at the same time. Which of the following choices identifies the study design used by the investigators? >>A) - (Correct) Cross-Sectional Study - Case Series Report - Cohort Study - Case-Control Study - Randomized Clinical Trial - Officials report increased incidence of acute lymphocytic leukemia (ALL) among children aged $\pu{5-12}$ in a community exposed to chemical waste from a nearby factory. If a study is designed to evaluate the claim, which of the following subjects are most likely to comprise the control group? >>A) - (Correct) Children from the outpatient clinic who do not suffer from ALL - Children exposed to the chemical waste who do not suffer from ALL - Children not exposed to the chemical waste who do not suffer from ALL - Children not exposed to the chemical waste who suffer from ALL - Children who suffered from ALL but got cured - $\pu{500 women}$ aged $\pu{40-54}$ are asked about meat consumption; 20% are vegetarian. During the ensuing $\pu{5 years}$, $\pu{5 vegetarians}$ and $\pu{43 non-vegetarians}$ develop colorectal cancer. Which of the following best describes the study design? >>A) - (Correct) Cohort Study - Case Series Report - Case-Control Study - Cross-Sectional Study - Randomized Clinical Trial - A group of researchers wants to investigate an outbreak of acute diarrhea that occurred in a small coastal town. They believe the outbreak is related to seafood prepared at one specific restaurant. Which of the following study designs is most appropriate to investigate the hypothesis? >>A) - (Correct) Case-control study - Cohort study - Cross-sectional study - Ecologic study - Clinical trial - A study assesses the relationship between ethnicity and end-stage renal disease. Pathologists study kidney biopsies. One group is aware of the patient’s race, while the second group is blinded. The first group reports ‘hypertensive nephropathy’ much more frequently for black patients than the second group. Which of the following types of bias is most likely present in this study? >>A) - (Correct) Observer bias - Confounding - Nonresponse bias - Recall bias - Referral bias - A cohort study shows no association between high-fat diet and colorectal adenocarcinoma after controlling for risk factors: relative risk $1.35$ ($p = 0.25$). However, 40% of the high-fat group and 36% of the low-fat group were lost to follow-up. Which of the following biases is most likely to be present? >>A) - (Correct) Selection bias - Observer bias - Ascertainment bias - Recall bias - Confounding - A study interviews mothers whose children have neural tube defects and controls with unaffected children about pain reliever use during pregnancy. The study shows an increased risk: $OR = 1.5$, $p = 0.03$. Which of the following biases is of major concern when interpreting the results? >>A) - (Correct) Recall bias - Nonresponse bias - Susceptibility bias - Observer bias - Confounding - Investigators are planning a clinical trial to evaluate propranolol on portal hypertension outcomes. They are concerned that episodes of major gastrointestinal hemorrhage could be over-reported in the placebo group. Which of the following is the most useful technique to reduce this possibility? >>A) - (Correct) Blinding - Randomization - Matching - Restriction - Stratified analysis - Diabetics are twice as likely to die from myocardial infarction as non-diabetics. A case-control study conducted in survivors identifies $\pu{1,000 people}$ with MI and $\pu{1,000}$ without. According to the results, diabetes has a protective effect against MI. Which of the following best explains the observed study results? >>A) - (Correct) Selection bias - Latent period - Observer bias - Hawthorne effect - Recall bias - A case-control study finds alcohol consumption is associated with lung cancer ($OR = 2.25$). However, when subjects are divided into smokers and non-smokers, no association is found within either group. The scenario is an example of: >>A) - (Correct) Confounding - Observer bias - Placebo effect - Selective survival - Nonresponse bias - A cohort study shows that in women with a family history of breast cancer, oral contraceptive use increases the risk of breast cancer ($RR = 2.10, p = 0.04$). In women without a family history, no effect is observed ($RR = 1.05, p = 0.40$). The phenomenon described is an example of: >>A) - (Correct) Effect modification - Confounding - Selection bias - Latent period - Selective survival - A case-control study evaluates the association between alcohol consumption and oral cavity cancer. Smoking is considered a potential confounder. Which of the following properties of smoking is essential in order for it to be considered as a confounder? >>A) - (Correct) It must be related to alcohol consumption - It must not be related to cancer of the oral cavity - It must be prevalent in the population of interest - It must be observed only in alcohol consumers - It must not be controlled for in the analysis - A case-control study assesses alcohol consumption and breast cancer. Investigators interview patients and then select neighbors of the same age and race as controls. This helps minimize which problem? >>A) - (Correct) Confounding - Selection bias - Recall bias - Observer’s bias - Effect modification - In a study where cirrhotic patients are randomly assigned to propranolol or placebo using a computer, this strategy is most helpful for controlling which of the following? >>A) - (Correct) Confounding - Placebo effect - Recall bias - Selective survival - Effect modification (interaction) - A clinical trial evaluating a beta-blocker for heart failure uses a design where neither the patient nor clinicians are aware of the drug assignment. This feature is used to prevent: >>A) - (Correct) Placebo effect and observer bias - Placebo effect and nonresponse bias - Recall bias and confounding - Confounding and defaulting - Lead-time bias and non-compliance - A trial for a new aldosterone antagonist uses ‘intention-to-treat’ analysis. Which of the following is the best statement concerning the benefits of ‘intention-to-treat’? >>A) - (Correct) Preserves the advantages of randomization - Decreases placebo effect - Decreases observer’s bias - Measures the degree of non-compliance - Increases the power of the study - A clinical trial includes a table showing that treatment and placebo groups have similar distributions of baseline characteristics (age, race, hypertension prevalence, etc). This best reflects that: >>A) - (Correct) Randomization is successful - Sample size is adequate - The study is negative - The power of the study is high - Observer’s bias might be an issue - In a study of $\pu{400 patients}$ with diabetes, serum cholesterol is normally distributed with a mean of $\pu{230 mg/dL}$ and standard deviation of $\pu{10 mg/dL}$. How many patients do you expect to have serum cholesterol $\ge \pu{250 mg/dL}$? >>A) - (Correct) 10 - 2 - 20 - 64 - 128 - In a study where serum cholesterol is normally distributed with a mean of $\pu{230 mg/dL}$ and standard deviation of $\pu{10 mg/dL}$, 95% of observations lie between which limits? >>A) - (Correct) 210 and 250 mg/dL - 220 and 240 mg/dL - 225 and 235 mg/dL - 200 and 260 mg/dL - 220 and 260 mg/dL - If the population mean blood glucose level is subtracted from a patient’s level, and the result is divided by the standard deviation, the value obtained is the: >>A) - (Correct) Z score - T score - F value - Chi-square value - Correlation coefficient - In a positively skewed distribution (tail to the right), which is the correct order of the values, from lowest to highest? >>A) - (Correct) Mode, Median, Mean - Mode, Mean, Median - Mean, Median, Mode - Mean, Mode, Median - Median, Mode, Mean - Median, Mean, Mode - An investigator compares an average standardized depression score in two groups of hypertensive patients: those who take beta-blockers and those who do not. Which test is used to analyze the results? >>A) - (Correct) Two-sample t test - Paired t test - Fisher’s exact test - Pearson’s chi-square test - Analysis of variance - Spearman’s correlation coefficient - A study presents data on HRT use and serum CRP (categorized as “high” or “normal”):

Which is the best statistical method to assess the association? >>A) - (Correct) Pearson’s chi-square test - Paired t test - Two-sample t test - Fisher’s exact test - Analysis of variance - Spearman’s correlation coefficient - Body mass index of $\pu{100 patients}$ is calculated at baseline and compared to the value after $\pu{1 year}$ of treatment with a new drug. Which test is used? >>A) - (Correct) Paired t test - Two-sample t test - Fisher’s exact test - Pearson’s chi-square test - Analysis of variance - Spearman’s correlation coefficient - A study evaluates thymectomy in $\pu{9 patients}$ (7 improved) versus conservative treatment in $\pu{20 patients}$ (8 improved). Which test is used to analyze the study results? >>A) - (Correct) Fisher’s exact test - Paired t test - Two-sample t test - Pearson’s chi-square test - Analysis of variance - Spearman’s correlation coefficient - Survival information for patients on a new chemotherapy regimen: * $\pu{0-1 months}$: $\pu{200 patients}$ at start, $\pu{20 deaths}$ (10%) * $\pu{1-2 months}$: $\pu{180 patients}$ at start, $\pu{10 deaths}$ (5.6%) * $\pu{2-3 months}$: $\pu{170 patients}$ at start, $\pu{12 deaths}$ (7%)

What is the probability that a patient on the new regimen is alive at $\pu{3 months}$? >>A) - (Correct) 0.9 * 0.94 * 0.93 - 0.93 - 0.89 - (0.9 + 0.94 + 0.93)/3 - 1 - 0.89 * 0.86 - In a stomach cancer trial, 80% of patients in both the treatment and placebo groups die by $\pu{24 months}$. Yet, investigators conclude the treatment is effective. Which is the most likely explanation? >>A) - (Correct) Time-to-event data were analyzed - Observer bias may be present - Selective survival may be an issue - The results are confounded - Two-year risk was calculated - A multi-vitamin trial shows parallel survival curves for the first $\pu{3 years}$ before they separate in favor of the treatment group. This demonstrates: >>A) - (Correct) Latent period - Multi-vitamin use is ineffective - Inappropriate selection of subjects - The follow-up period is too long - The sample size is not large enough - A hypolipidemic drug trial ($\pu{n = 1000}$) fails to show a significant difference ($p = 0.09$) for a rare side effect (acute myositis), even though other small trials reported it. The failure to detect significance is most likely due to: >>A) - (Correct) Small sample size - Selection bias - Short follow-up period - Inappropriate selection of patients - Observer’s bias - What is the best method to investigate a rare side effect that was reported but was not statistically significant in several individual clinical trials? >>A) - (Correct) Pool the data from several trials (Meta-analysis) - Conduct a new large-scale clinical trial - Review medical charts to re-ascertain events - Do stratified analysis on multiple risk-factors - Ignore the possible association - What is the probability that a prospective study will show an association if in fact a protective effect of hormone replacement therapy on dementia risk exists in reality? >>A) - (Correct) $1 - \beta$ - $\alpha$ - $\beta$ - $1 - \alpha$ - Type I error - Type II error - Two doctors hear crackles in an HIV-positive patient, but a third doctor reports clear lungs. Which phrase best describes the role of auscultation as a diagnostic tool in this case? >>A) - (Correct) Not reliable - Not valid - Not sensitive - Not specific - Not accurate - A study fails to demonstrate an association between chemical exposure and pancreatic cancer. Which of the following does NOT affect the validity of the study? >>A) - (Correct) Sample size - Selection bias - Differential misclassification - Confounding