# Confidence Interval for a Proportion

The applet below illustrates the concept of constructing confidence intervals for proportions (a 1-proportion z-interval). Set the population proportion, sample size, and confidence level using the sliders. There are 100 confidence intervals at your chosen confidence level, based on 100 random samples of your chosen sample size, from a population with your chosen proportion. On average, the percentage of confidence intervals that contain the population proportion will be equal to the chosen confidence level. You will notice that larger sample sizes produce shorter confidence intervals (why?). You will notice that larger confidence levels produce longer confidence intervals (why?)