1.9 Confidence Intervals

A confidence interval is a range of numbers produced by a method that is likely to include the true value of the population. For example, you might measure a sample of women in your class and find that their average shoe size is about a size 8 with a standard deviation of 1.5 shoe sizes. From this information we can calculate that there is a 68% chance that the population of women has a shoe size between size 6.5 and 9.5 (which is one standard deviation from the sample mean) and that there is a 95% chance that the population shoe size is between 5 and 11 (which is two standard deviations from the sample mean). This is our confidence interval.