NBME Biostatistics and Epidemiology

Question 1

A dataset has a mean, median, and mode that are all equal. Which of the following BEST describes this distribution?

Accepted Answer

Normal (bell-shaped)

Answer

Positively skewed

Answer

Negatively skewed

Answer

Bimodal

Question 2

A screening test has 90% sensitivity and 80% specificity. The disease prevalence is 10%. What is the approximate positive predictive value (PPV)?

Accepted Answer

33%

Answer

50%

Answer

80%

Answer

90%

Question 3

Which measure of central tendency is MOST affected by extreme outliers in a dataset?

Accepted Answer

Mean

Answer

Mode

Answer

Median

Answer

Interquartile range

Question 4

A study reports a p-value of 0.03 with alpha set at 0.05. What is the correct interpretation?

Accepted Answer

There is a 3% probability of obtaining results this extreme if the null hypothesis is true

Answer

There is a 3% probability the null hypothesis is true

Answer

The study has 97% statistical power

Answer

The finding is clinically significant

Question 5

The Number Needed to Treat (NNT) is calculated as:

Accepted Answer

1 / Absolute Risk Reduction

Answer

1 / Relative Risk Reduction

Answer

Absolute Risk Reduction × 100

Answer

Relative Risk / Absolute Risk

Question 6

A researcher compares mean systolic blood pressure between a drug group and a placebo group (continuous outcome, two independent groups, normally distributed). Which statistical test is MOST appropriate?

Accepted Answer

Student's t-test

Answer

Chi-squared test

Answer

Pearson correlation

Answer

Kaplan-Meier analysis

Question 7

Type I error (α) in hypothesis testing is defined as:

Accepted Answer

Rejecting a true null hypothesis

Answer

Failing to reject a false null hypothesis

Answer

Having insufficient power to detect a true effect

Answer

Using an inappropriately small sample size