public static function cohensQ($r₁, $r₂) { if ($r₁ >= 1 || $r₂ >= 1) { throw new Exception\OutOfBoundsException('r must be greater than or equal to 1'); } $½ = 0.5; return abs($½ * log((1 + $r₁) / (1 - $r₁)) - $½ * log((1 + $r₂) / (1 - $r₂))); }