Excel like a finance pro.
Statistical function
CONFIDENCE.T
Returns the confidence interval for a population mean using a Student t distribution.
When to use it
The half-width of a confidence interval for a mean using the t distribution, for when the standard deviation is estimated from a small sample.
The shape of it
- Syntax
=CONFIDENCE.T(alpha, standard_dev, size)
Worked examples
95% interval
=CONFIDENCE.T(0.05,2.5,50) → 0.710493
Slightly wider than CONFIDENCE.NORM on the same inputs.
Larger sample
=CONFIDENCE.T(0.05,15,100) → 2.976326
With 100 observations the t and normal versions are close.
Small sample
=CONFIDENCE.T(0.05,1,10) → 0.715351
A small sample: the t distribution widens the interval.
Worth knowing
- Use this by default for sample data; the normal version is for known population sd.
- Interval is mean ± result.
- Replaces the manual T.INV.2T(alpha,n-1)*sd/SQRT(n).
Where it goes wrong
- #NUM! when size is less than 2 or sd is not positive.
- #DIV/0! when size is 1.
Related
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