Biostatistics and Epidemiology Flashcards

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

Answer: Normal (bell-shaped)

When mean, median, and mode are equal, the distribution is symmetric and follows a normal (Gaussian) bell-shaped curve.

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

Answer: 33%

PPV = (sensitivity × prevalence) / [(sensitivity × prevalence) + (1−specificity)(1−prevalence)] = (0.9×0.1) / (0.9×0.1 + 0.2×0.9) ≈ 33%.

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

Answer: Mean

The mean uses all values in its calculation, so a single extreme outlier can substantially shift it, unlike the median or mode.

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

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

A p-value represents the probability of observing results at least as extreme as those found, assuming the null hypothesis is true — not the probability that the null is true.

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

Answer: 1 / Absolute Risk Reduction

NNT = 1 / ARR; it tells you how many patients must be treated to prevent one adverse outcome compared to control.

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?

Answer: Student's t-test

The Student's t-test is used to compare means between two independent groups when data are normally distributed.

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

Answer: Rejecting a true null hypothesis

A Type I error (false positive) occurs when the null hypothesis is actually true but is incorrectly rejected; its probability equals α.