Question

Find the minimum sample size required to estimate the population proportion p: Margin of error: 0.20; confidence level: 92%; begin mathsize 14px style p with hat on top end style and begin mathsize 14px style q with hat on top end style are not known. Your answer must be an integer.

Answer 1

`n=(\hat p (1-\hat p))/(((ME)/(z))^2)` (b)

And replacing into equation (b) the values from part a we got:

`n=(0.5(1-0.5))/(((0.2)/(1.75))^2)=19.14`

And rounded up we have that n=20

Explanation:

Previous concepts

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

The population proportion have the following distribution

`p \sim N(p,\sqrt{(p(1-p))/(n)})`

Solution to the problem

In order to find the critical value we need to take in count that we are finding the interval for a proportion, so on this case we need to use the z distribution. Since our interval is at 92% of confidence, our significance level would be given by
`\alpha=1-0.92=0.08` and
`\alpha/2 =0.04`. And the critical value would be given by:

`z_(\alpha/2)=-1.75, z_(1-\alpha/2)=1.75`

Since we don't know the estimated proportion we can use
`\hat p =0.5`

The margin of error for the proportion interval is given by this formula:

`ME=z_(\alpha/2)\sqrt{(\hat p (1-\hat p))/(n)}` (a)

And on this case we have that
`ME =\pm 0.2` and we are interested in order to find the value of n, if we solve n from equation (a) we got:

`n=(\hat p (1-\hat p))/(((ME)/(z))^2)` (b)

And replacing into equation (b) the values from part a we got:

`n=(0.5(1-0.5))/(((0.2)/(1.75))^2)=19.14`

And rounded up we have that n=20