Confidence Intervals for the Mean

This section explains the need for confidence intervals and why a confidence interval is not the probability the interval contains the parameter. Then, it discusses how to compute a confidence interval on the mean when sigma is unknown and needs to be estimated. It also explains when to use t-distribution or a normal distribution. Next, it covers the difference between the shape of the t distribution and the normal distribution and how this difference is affected by degrees of freedom. Finally, it explains the procedure to compute a confidence interval on the difference between means.

Confidence Intervals Introduction


  1. This is the most accurate interpretation of a 95% confidence interval.

  2. Confidence intervals can be computed for various parameters, not just the mean. Later in this chapter you will see how to compute a confidence interval for the population correlation.