In: Statistics and Probability
A market research firm is hired to perform a survey and analyze the true proportion of the households with pets. How many households should they survey in order to be 90% confident that the estimated (sample) proportion is within two percentage points of the true population? Assume that pq = 0.25
Solution :
Given that,
pq = 0.25
margin of error = E = 0.02
At 90% confidence level the z is ,
= 1 - 90% = 1 - 0.90 = 0.10
/ 2 = 0.10 / 2 = 0.05
Z/2 = Z0.05 = 1.645
sample size = n = (Z / 2 / E )2 * pq
= (1.645 / 0.02)2 * 0.25
= 1691.27
sample size = 1692