Question

An investigator wants to estimate caffeine consumption in high school students. how many students would be required to estimate the proportion of students who consume coffee? suppose we want the estimate to be within 5% of the true proportion with 95% confidence.

Answer 1

We can solve this problem by referring to the standard probability distribution tables for z.

We are required to find for the number of samples given the proportion (P = 5% = 0.05) and confidence level of 95%. This would give a value of z equivalent to:

z = 1.96

Since the problem states that it should be within the true proportion then p = 0.5

Now we can find for the sample size using the formula:

n = (z^2) p q /E^2

where,

 p = 0.5

q = 1 – p = 0.5

E = estimate of 5% = 0.05

Substituting:

n = (1.96^2) 0.5 * 0.5 / 0.05^2

n = 384.16

Around 385students are required.