# Estimating Proportions

#### cannoli

##### New Member
Does anyone know any good sites fro explaining estimating proportions? I am clueless as to how to do this. My notes are not helping me. Is there a way to do the calculations with a TI-83 Plus?

The American Heart Association is conducting an ad campaign. The Association wants to know the fraction of American smokers over the age of 21.

Suppose a sample of 292 Americans is drawn. Out of these people 243 do not smoke. Using the data estimate the proportion of Americans over 21 who smoke.

#### BioStatMatt

##### TS Contributor
Well if the sample can be thought of as a representative sample from all Americans over 21. Then the estimated proportion of Americans over 21 who smoke is:

(number in sample who smoke) / (total in sample) = (292-243) / 292= 0.168

~Matt

#### pierre.fasciola

##### New Member
We can calculate the 95% confidence interval for the ratio.

SE = sqrt[p(1-p)/N] = sqrt(0.168*0.832/292) = 0.02188

95% confidence interval = 0.168 +/- 1.96 SE = 0.125 to 0.211