CRA Biostatistics & Hypothesis Testing 3

Question 1

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

Accepted Answer

A significant result at alpha=0.05

Answer

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.

Question 2

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

Accepted Answer

t-distribution

Answer

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

Question 3

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

Accepted Answer

A strong negative linear relationship

Answer

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

Question 4

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

Accepted Answer

1 / Absolute risk reduction

Answer

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

Question 5

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

Accepted Answer

The exposed and unexposed groups have equal risk

Answer

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

(CRA) Certified Research Associate Practice Test

(CRA) Certified Research Associate Practice Test

CRA Biostatistics & Hypothesis Testing 3