In: Statistics and Probability
Suppose the manager of a shoe store wants to determine the current percentage of customers who are males. How many customers should the manager survey in order to be 99% confident that the estimated (sample) proportion is within 10 percentage points of the true population proportion of customers who are males?
z0.10 z0.05 z0.04 z0.025 z0.01 z0.005 1.282 1.645 1.751 1.960 2.326 2.576
Solution :
Given that,
= 0.5
1 - = 1 - 0.5 = 0.5
margin of error = E = 10% = 0.010
At 99% confidence level the z is,
= 1 - 99%
= 1 - 0.99 = 0.01
/2 = 0.005
Z/2 = 2.576 ( Using z table )
Sample size = n = (Z/2 / E)2 * * (1 - )
= (2.576 / 0.010)2 * 0.5 * 0.5
=16589.44
Sample size = 16590 rounded
n=16590 customers