T.INV
The value whose left-tail probability in Student's t distribution is the one given.
Group: Statistics. Compatible with DAX.
Syntax
T.INV ( <Probability>, <Deg_freedom> )| Parameter | Type | Description |
|---|---|---|
Probability | Number | The left-tail probability, strictly between 0 and 1. |
Deg_freedom | Whole number | The degrees of freedom, 1 or more; rounded to a whole number. |
Returns
Number. The t below which Student's t distribution holds the given probability.
Remarks
- The curve is symmetric:
T.INV ( 0.025, df )is minusT.INV ( 0.975, df ). T.INV ( 0.975, df )is the t of a two-sided 95 % interval, the same asT.INV.2T ( 0.05, df ).- A probability of 0 or 1 or beyond, or fewer than 1 degree of freedom, is an error.
Examples
The 2.5 % and 97.5 % points
EVALUATE
ROW ( "97.5 %", T.INV ( 0.975, 10 ), "2.5 %", T.INV ( 0.025, 10 ) )| 97.5 % | 2.5 % |
|---|---|
| 2.22813885198627 | -2.22813885198627 |
A 95 % interval for the mean month
EVALUATE
VAR Monthly = ADDCOLUMNS ( VALUES ( Sales[Month] ), "Liters", [Liters sold] )
VAR n = COUNTROWS ( Monthly )
VAR Mean = AVERAGEX ( Monthly, [Liters] )
VAR Margin = T.INV ( 0.975, n - 1 ) * STDEVX.S ( Monthly, [Liters] ) / SQRT ( n )
RETURN
ROW ( "Mean", Mean, "Lower", Mean - Margin, "Upper", Mean + Margin )| Mean | Lower | Upper |
|---|---|---|
| 50179.5277777778 | 47847.8481824441 | 52511.2073731114 |