Power Pivot Principles: The A to Z of DAX Functions – CONFIDENCE.T
21 June 2022
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:
CONFIDENCE.T(alpha, standard_dev, size)
- 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.
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