Question

6. A clinical trial is being planned to investigate the effect of a new experimental drug designed to reduce total serum cholesterol. Investigators will enroll participants with total cholesterol levels between 200-240, they will be randomized to receive the new drug or a placebo and followed for 2 months, and the total cholesterol will be measured. Investigators plan to estimate a confidence interval with a difference of 8 points in mean total cholesterol levels between groups. They assume that 10% of the participants randomized will be lost over the 2 month follow-up. How many participants must be enrolled in the study? Assume that the standard deviation of total cholesterol is 18.5.

Answer 1

Number of participants (n) is given by:

$n=\frac{Z_{\alpha /2}\times \sigma ^{2}}{e^{2}}$

Given:

$\alpha$ = 0.10

From Table, critical values of Z = $\pm$ 1.645

$\sigma$ = 18.5

e = 8

Substituting, we get:

$n=\frac{1.645^{2}\times 18.5^{2}}{8^{2}}=15$

So,

Answer is:

15