Question

How many subjects need to be sampled if we are estimating the population proportion and we want a 90% confidence level with the error of at most 2 percentage points?

Answer 1

Solution :

Given that,

= 0.5

1 - = 0.5

margin of error = E = 2% = 0.02

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05 = 1.645 ( Using z table )

Sample size = n = (Z/2 / E)2 * * (1 - )

= (1.645 / 0.02)2 * 0.5 * 0.5

=1691.26

Sample size = 1691