How to Compute the Confidence Interval on the Mean

Computing the confidence interval of a mean can be done if you know a few values ahead of time: the sampling distribution of the mean, the standard deviation, and the mean itself. The equation for the confidence interval is the mean plus or minus Z multiplied by the stand error of the mean, where Z is a constant depending on how large you want the confidence interval to be. For most studies, the confidence interval is 95%, making Z equal to 1.96.

Instructions

1

Calculate the square root of the sample size.

2

Divide the standard deviation by the square root of the sample size. This is the standard error of the mean.

3

Multiply the stand error by Z. If you wish to have a confidence interval of 95%, your Z will be 1.96.

4

Add the resulting value to the mean to calculate the high end of the interval. Subtract it from the mean to calculate the low end of the interval.