(PECL stats >= 1.0.0)
stats_cdf_t — Calculates any one parameter of the t-distribution given values for the others
$par1
, float $par2
, int $which
) : float
Returns the cumulative distribution function, its inverse, or one of its parameters,
of the t-distribution. The kind of the return value and parameters
(par1 and par2) are determined by
which.
The following table lists the return value and parameters by which.
CDF, x, and nu denotes cumurative distribution function, the value of the random
variable, and the degrees of freedom of the t-distribution, respectively.
which |
Return value | par1 |
par2 |
|---|---|---|---|
| 1 | CDF | x | nu |
| 2 | x | CDF | nu |
| 3 | nu | x | CDF |
par1The first parameter
par2The second parameter
whichThe flag to determine what to be calculated
Returns CDF, x, or nu, determined by which.
Input and return values of stats_cdf_t depends on the $which-parameter:
<?php
function get_t_p($t, $df){
return stats_cdf_t($t, $df, 1);
}
function get_t_t($p, $df){
return stats_cdf_t($p, $df, 2);
}
function get_t_df($p, $t){
return stats_cdf_t($p, $t, 3);
}
?>
In order to match the output of this function with Excel's TDIST function, you must take 1 - the value. For example, for a two-tailed T-distribution for x=4 and degrees of freedom=2, the formula would be:
(1 - stats_cdf_t(4, 2, 1)) * 2
For a single tail, do not include the multiply by 2 portion.