Power and sample size Practice Questions

Question 1

A 21-year-old man presents to the office for a follow-up visit. He was recently diagnosed with type 1 diabetes mellitus after being hospitalized for diabetic ketoacidosis following a respiratory infection. He is here today to discuss treatment options available for his condition. The doctor mentions a recent study in which researchers have developed a new version of the insulin pump that appears efficacious in type 1 diabetics. They are currently comparing it to insulin injection therapy. This new pump is not yet available, but it looks very promising. At what stage of clinical trials is this current treatment most likely at?

Accepted Answer

Phase 3

Answer

Phase 0

Answer

Phase 2

Answer

Phase 1

Answer

Phase 4

Question 2

An investigator is measuring the blood calcium level in a sample of female cross country runners and a control group of sedentary females. If she would like to compare the means of the two groups, which statistical test should she use?

Accepted Answer

t-test

Answer

Chi-square test

Answer

Linear regression

Answer

ANOVA (Analysis of Variance)

Answer

F-test

Question 3

A research team is studying the effects of a novel drug that was discovered to treat type 2 diabetes. In order to learn more about its effects, they follow patients who are currently taking the drug and determine whether there are adverse effects that exceed anticipated levels and may therefore be drug-related. They discover that the drug causes an excess of sudden cardiac death in 19 patients with renal failure out of 2 million total patients that are followed. Based on these results, an additional warning about this serious adverse effect is added to the investigator brochure for the drug. Which of the following clinical phase studies does this study most likely describe?

Accepted Answer

Phase IV

Answer

Phase II

Answer

Phase V

Answer

Phase III

Answer

Phase I

Question 4

You are reading through a recent article that reports significant decreases in all-cause mortality for patients with malignant melanoma following treatment with a novel biological infusion. Which of the following choices refers to the probability that a study will find a statistically significant difference when one truly does exist?

Accepted Answer

Power

Answer

Type II error

Answer

Type I error

Answer

Confidence interval

Answer

p-value

Question 5

An epidemiologist is evaluating the efficacy of Noxbinle in preventing HCC deaths at the population level. A clinical trial shows that over 5 years, the mortality rate from HCC was 25% in the control group and 15% in patients treated with Noxbinle 100 mg daily. Based on this data, how many patients need to be treated with Noxbinle 100 mg to prevent, on average, one death from HCC?

Accepted Answer

10

Answer

20

Answer

73

Answer

50

Answer

100

Question 6

The height of American adults is expected to follow a normal distribution, with a typical male adult having an average height of 69 inches with a standard deviation of 0.1 inches. An investigator has been informed about a community in the American Midwest with a history of heavy air and water pollution in which a lower mean height has been reported. The investigator plans to sample 30 male residents to test the claim that heights in this town differ significantly from the national average based on heights assumed be normally distributed. The significance level is set at 10% and the probability of a type 2 error is assumed to be 15%. Based on this information, which of the following is the power of the proposed study?

Accepted Answer

0.85

Answer

0.10

Answer

0.90

Answer

0.15

Answer

0.05

Question 7

A scientist is designing a study to determine whether eating a new diet is able to lower blood pressure in a group of patients. In particular, he believes that starting the diet may help decrease peak blood pressures throughout the day. Therefore, he will equip study participants with blood pressure monitors and follow pressure trends over a 24-hour period. He decides that after recruiting subjects, he will start them on either the new diet or a control diet and follow them for 1 month. After this time, he will switch patients onto the other diet and follow them for an additional month. He will analyze the results from the first month against the results from the second month for each patient. This type of study design is best at controlling for which of the following problems with studies?

Accepted Answer

Confounding

Answer

Hawthorne effect

Answer

Recall bias

Answer

Selection bias

Answer

Pygmalion effect

Question 8

A first-year medical student is conducting a summer project with his medical school's pediatrics department using adolescent IQ data from a database of 1,252 patients. He observes that the mean IQ of the dataset is 100. The standard deviation was calculated to be 10. Assuming that the values are normally distributed, approximately 87% of the measurements will fall in between which of the following limits?

Accepted Answer

85–115

Answer

95–105

Answer

65–135

Answer

80–120

Answer

70–130

Question 9

The mean, median, and mode weight of 37 newborns in a hospital nursery is 7 lbs 2 oz. In fact, there are 7 infants in the nursery that weigh exactly 7 lbs 2 oz. The standard deviation of the weights is 2 oz. The weights follow a normal distribution. A newborn delivered at 10 lbs 2 oz is added to the data set. What is most likely to happen to the mean, median, and mode with the addition of this new data point?

Accepted Answer

The mean will increase; the median will stay the same; the mode will stay the same

Answer

The mean will increase; the median will increase; the mode will stay the same

Answer

The mean will stay the same; the median will increase; the mode will stay the same

Answer

The mean will increase; the median will increase; the mode will increase

Answer

The mean will stay the same; the median will increase; the mode will increase

Question 10

Many large clinics have noticed that the prevalence of primary biliary cholangitis (PBC) has increased significantly over the past 20 years. An epidemiologist is working to identify possible reasons for this. After analyzing a series of nationwide health surveillance databases, the epidemiologist finds that the incidence of PBC has remained stable over the past 20 years. Which of the following is the most plausible explanation for the increased prevalence of PBC?

Accepted Answer

Improved quality of care for PBC

Answer

Increased availability of diagnostic testing for PBC

Answer

Increased exposure to environmental risk factors for PBC

Answer

Increased awareness of PBC among clinicians

Answer

Increased average age of the population at risk for PBC

Power and sample size

Study Resources

Lessons

Questions

Flashcards

Lessons

Statistical power definition

Type I and Type II errors

Factors affecting power

Sample size calculation for different study designs

Effect size estimation

Minimally important difference

Sample size for non-inferiority trials

Sample size for equivalence trials

Power calculations for subgroup analyses

Post-hoc power analysis limitations

Adaptive sample size methods

Power for repeated measures designs

Group sequential designs

Practice Questions

Flashcards

About Power and sample size for USMLE

Lessons in Power and sample size

Master Power and sample size