In: Statistics and Probability
A private opinion poll is conducted for a politician to determine what proportion of the population favors decriminalizing marijuana possession. How large a sample is needed in order to be
92%
confident that the sample proportion will not differ from the true proportion by more than
5%
?
Solution,
Given that,
= 1 - = 0.5
margin of error = E = 0.05
At 92% confidence level
= 1 - 92%
= 1 - 0.92 =0.08
/2
= 0.04
Z/2
= Z0.04 = 1.751
sample size = n = (Z / 2 / E )2 * * (1 - )
= (1.751 / 0.05)2 * 0.5 * 0.5
= 306.60
sample size = n = 307