Question

A certain survey conducted had a population proportion of at most 22% for people who agreed. What is the confidence level if 20% of the people sampled agreed, and the standard error of the proportion is ±1%?

Answer 1

The formula for the population proportion is:

n = p ± Zc
`√((p(1-p)/n))`

where p = confidence level = 0.2

n = proportion = 0.22

`√((p(1-p)/n))` = standard error = 0.01

Finding for Zc:

.20+(.01)=.22

Zc = 2

Referring to Critical value table for standard normal curve, a Zc value of 2 is equivalent to 95% Confidence Level.

Answer: 95% Confidence Level