Recently, I used this PHP class in one of my projects. It is very useful, well-prepared and works great except one minor problem that I noticed. Standard deviation is miscalculated when you call the corresponding function.
When I checked the code, I realized it is due to the structure of the array causing the problem and make the output different than the STDEV function in Microsoft Excel.
I present the very quick fix of it for those who are also using this function.
$mean = $this->mean;
$XminA = array();
foreach($this->scores as $key => $val) {
($sqr == true) ? $XminA[$val] = round(pow(($val - $mean),2),$this->round) : $XminA[$val] = round(($val - $mean),$this->round);
}
if($sqr == true) {
$mean = $this->mean;
$XminA = array();
foreach($this->scores as $key => $val) {
($sqr == true) ? $XminA[$key] = round(pow(($val - $mean),2),$this->round) : $XminA[$key] = round(($val - $mean),$this->round);
}
if($sqr == true) {
Soon after I wrote this article, I realized the developer (Nathan Poultney) released the new version of the class.
Thanks for the update!