Confidence intervals for proportions

We build a confidence interval for a proportion when we want to estimate what percent of a population fits some category. For example, what percent of voters support a certain candidate? Instead of polling everyone, we can take a sample and make an estimate using a confidence interval.

Conditions for valid confidence intervals for a proportion

Conditions for confidence interval for a proportion worked examples

Conditions for a z interval for a proportion

Critical value (z*) for a given confidence level

Finding the critical value z* for a desired confidence level

Example constructing and interpreting a confidence interval for p

Calculating a z interval for a proportion

Determining sample size based on confidence and margin of error

Sample size and margin of error in a z interval for p