Question

Create a 90% confidence interval about a sample proportion given that the sample proportion is .61 and the sample size is 1250.

Answer 1

Solution :

Given that,

n = 1250

Point estimate = sample proportion = = 0.61

1 - = 1 - 0.61 = 0.39

At 90% confidence level

= 1 - 90%

=1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05  = 1.645

Margin of error = E = Z / 2 * (( * (1 - )) / n)

= 1.645 (((0.61 * 0.39) / 1250 )

= 0.023

A 90% confidence interval for population proportion p is ,

± E

= 0.61  ± 0.023

= ( 0.587, 0.633 )