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# A to Z of Excel Functions: the CONFIDENCE.T Function

11 October 2017

Welcome back to our regular A to Z of Excel Functions blog.  Today we look at the CONFIDENCE.T function.

The CONFIDENCE.T function

Have you got your CONFIDENCE down to a T?  This function first appeared in Excel 2010 but unlike CONFIDENCE.NORM there was no equivalent in earlier versions of Excel.  That is because this 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