What is a confidence interval?

Using the normal distribution, we can estimate a range of values which we expect to contain the mean. For example, if we take a sample of 30 students height, we can estimate the mean height of students in the year group to lie within a certain range.

We can use different values of the normal distribution to change the accuracy of the confidence interval, for example either the 99% confidence interval or the 90% confidence interval. The greater the percentage confidence we use, the wider the interval will be.