stats_cdf_t

(PECL stats >= 1.0.0)

stats_cdf_t — Calculates any one parameter of the t-distribution given values for the others

Description

stats_cdf_t(float $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 cumulative distribution function, the value of the random variable, and the degrees of freedom of the t-distribution, respectively.

**Return value and parameters**
`which`	Return value	`par1`	`par2`
1	CDF	x	nu
2	x	CDF	nu
3	nu	x	CDF

Parameters

par1: The first parameter
par2: The second parameter
which: The flag to determine what to be calculated

Return Values

Returns CDF, x, or nu, determined by which.

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User Contributed Notes 2 notes

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Brian ¶

13 years ago

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.

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-4

Anonymous ¶

12 years ago

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);
}
?>

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