Question

A researcher wishes to estimate the proportion of adults who have high-speed Internet access. What size sample should be obtained if she wishes the estimate to be within 0.01 with 90% confidence if 

(a) she uses a previous estimate of 0.46? 

(b) she does not use any prior estimates? 

Answer 1

Sample size = Z²/2 * p (1 - p) / E²

a)

Given p= 0.46

Sample size = 1.6449² * 0.46 * 0.54 / 0.01²

= 6720.9

Sample size = 6721 (Rounded up to nearest integer)

b)

When prior estimate of proportion is not specified then p = 0.50

Sample size = 1.6449² * 0.50 * 0.50 / 0.01²

= 6764.24

Sample size = 6765 (Rounded up to nearest integer)