Power Pivot Principles: The A to Z of DAX Functions – CONFIDENCE.T

In our long-established Power Pivot Principles articles, we continue our series on the A to Z of Data Analysis eXpression (DAX) functions. This week, we look at CONFIDENCE.T.

The CONFIDENCE.T function

Have you got your CONFIDENCE down to a T?  This DAX function returns the confidence interval for a population mean, using a Student’s t distribution.

The CONFIDENCE.T function employs the following syntax to operate:

• alpha: this is required.  This represents the significance level used to compute the confidence level.  The confidence level equals 100*(1 - alpha)%, or in other words, an alpha of 0.05 indicates a 95 percent confidence level
• standard_dev: this is also required.  This is the population standard deviation for the data range and is assumed to be known
• size: also required. This is the sample size.

It should be further noted that:

• if any argument is non-numeric, CONFIDENCE.T returns the #VALUE! error value
• if alpha is ≤ 0 or ≥ 1, CONFIDENCE.T returns the #NUM! error value
  
• if standard_dev ≤ 0, CONFIDENCE.T returns the #NUM! error value
  
• if size is not an integer, it is truncated
• if size < 1, CONFIDENCE.T returns the #DIV/0! error value
• this function is not supported for use in DirectQuery mode when used in calculated columns or row-level security (RLS) rules.

Please see my example below:

i.e. for an alpha of 5% (or a confidence interval of 95%), with a standard deviation of the population of 3.0 and a sample size of 100 (for Student’s t distribution), the confidence interval around the sample mean will be 0.5953.

Come back next week for our next post on Power Pivot in the Blog section. In the meantime, please remember we have training in Power Pivot which you can find out more about here. If you wish to catch up on past articles in the meantime, you can find all of our Past Power Pivot blogs here.