/**
* Trimean (TM, or Tukey's trimean)
* A measure of a probability distribution's location defined as
* a weighted average of the distribution's median and its two quartiles.
* https://en.wikipedia.org/wiki/Trimean
*
* Q₁ + 2Q₂ + Q₃
* TM = -------------
* 4
*
* @param array $numbers
* @return number
*/
public static function trimean(array $numbers)
{
$quartiles = Descriptive::quartiles($numbers);
$Q₁ = $quartiles['Q1'];
$Q₂ = $quartiles['Q2'];
$Q₃ = $quartiles['Q3'];
return ($Q₁ + 2 * $Q₂ + $Q₃) / 4;
}