Biostatistics & Hypothesis Testing Flashcards

Confidence intervals and hypothesis tests are related in that a 95% CI for a difference that does NOT include zero corresponds to:

Answer: A significant result at alpha=0.05

A 95% CI excluding the null value (zero for a difference) is equivalent to rejecting the null hypothesis at alpha=0.05 with a two-tailed test.

Which distribution is used when the population standard deviation is unknown and the sample size is small?

Answer: t-distribution

The t-distribution accounts for additional uncertainty from estimating σ with s and has heavier tails than the normal distribution, particularly with small samples.

Pearson's correlation coefficient (r) ranges from −1 to +1. A value of r = −0.85 indicates:

Answer: A strong negative linear relationship

An r of −0.85 is close to −1, indicating a strong negative (inverse) linear association between the two variables.

In a randomized controlled trial, the number needed to treat (NNT) is calculated as:

Answer: 1 / Absolute risk reduction

NNT = 1 / ARR, where ARR is the absolute risk reduction (control event rate minus treatment event rate).

A study reports a relative risk (RR) of 1.0. This means:

Answer: The exposed and unexposed groups have equal risk

RR = 1.0 indicates no difference in risk between the exposed and unexposed groups, implying no association.

Which type of variable is best described as having ordered categories with unequal intervals between them?

Answer: Ordinal

Ordinal variables have a natural order (e.g., mild/moderate/severe) but the intervals between categories are not necessarily equal.

A researcher increases the sample size from 100 to 400 while all other factors remain constant. The standard error of the mean will:

Answer: Decrease by half

SE = σ/√n; quadrupling n multiplies √n by 2, halving the SE.