Excel - Microsoft Excel CONFIDENCE.NORM Function

Description

The Excel CONFIDENCE.NORM function uses a Normal Distribution to calculate a confidence value that can be used to construct the confidence interval for a population mean, for a supplied probablity and sample size. It is assumed that the standard deviation of the population is known. 

The Confidence.Norm function is new to Excel 2010. However, this is simply a renamed version of the Confidence function, which is available in earlier versions of Excel. 

The format of the function is : 

CONFIDENCE.NORM( alpha, standard_dev, size ) 

where the arguments are listed in the table below : 

To calculate the confidence interval for a population mean, the returned CONFIDENCE value must then be added to, and subtracted from, the sample mean. ie. for the sample mean x : 

Confidence Interval = x ± CONFIDENCE 

Confidence.Norm Function Example

In the spreadsheet below, the Excel Confidence.Norm Function is used to calculate the confidence interval, with a significance of 0.05 (ie. a confidence level of 95%), for the mean of a sample of heights of 100 men. The sample mean is 1.8 meters and the standard deviation is 0.07 meters. 

The above function returns a confidence value of 0.013719748

Therefore the confidence interval is 1.8 ± 0.013719748, which is equal to : 

1.786280252 to 1.813719748 

Confidence.Norm Function Common Errors

If you get an error from your Excel Confidence.Norm function this is likely to be one of the following : 

Common Errors