The Range F4:G5 shows us the standard deviation and count of the range: we will use these to find the confidence limits: Look at the images below as we work through an example to explore these ideas.įirst of all: there are just 31 data points and they could relate to anything! They occupy the range A3:B34, including column headings:

With a 5% significance level, we can say that we are confident that the mean value should lie somewhere in 95% of our data sample: that is, 47.5% either side of the mean. What a confidence limit does is it uses the behaviour of the Normal Distribution function and helps us to find, for example, the lower and upper value from a range of values within which the mean is probably going to be found. Typically a 5% confidence limit is prepared, as is a 90% and a 99% limit.

Excel Techniques Used in this Article =AVERAGE(), =STDEV(), =COUNT(), =NORMSDIST(), =CONFIDENCE.NORM(), normal distribution, mean (average), standard deviation, sample size, significance level, upper and lower confidence intervals, z value, range nameĬonfidence intervals or limits can be prepared for almost any significance level you like.