How do you construct a confidence interval?

A confidence interval for a statistical measure (range) is used to quantify the amount of uncertainty associated with a sample estimate of a population parameter. It is computed as Estimate ± Margin of Error. In a 95 percent confidence interval, for example, 95 percent of the samples are within the calculated population parameters.

1. Estimate the population parameter

   Use a simple random sample from the population to estimate the population parameter. Calculate the statistic that corresponds to the parameter of interest.

2. Select a confidence level

   Confidence level describes the uncertainty of a sampling method. In many cases, 90 percent, 95 percent, or 99 percent confidence levels are used, but any percentage can be used in practice.

3. Find the margin of error

   To find the margin of error, compute the critical value times the standard deviation of the statistic.

4. Determine the confidence interval

   The confidence interval is found by calculating the mean estimate ± the margin of error.