MDL-16951 "kurtosis and skewness equations were wrong" See changes to equations here...

diff --git a/mod/quiz/report/statistics/report.php b/mod/quiz/report/statistics/report.php
index cb70bb911741e5e8d6fb5f99e6b0609251d55bfb..c5413f2b87820a63aa8f6de90439e6b3cd1b427d 100644 (file)
--- a/mod/quiz/report/statistics/report.php
+++ b/mod/quiz/report/statistics/report.php
@@ -547,13 +547,13 @@ class quiz_statistics_report extends quiz_default_report {
                     $k2= $s*$m2/($s-1);
                     $k3= $s*$s*$m3/(($s-1)*($s-2));
                     if ($k2){
-                        $quizstats->skewness = $k3 / (pow($k2, 2/3));
+                        $quizstats->skewness = $k3 / (pow($k2, 3/2));
                     }
                 }
     
     
                 if ($s>3){
-                    $k4= (($s*$s*$s)/(($s-1)*($s-2)*($s-3)))*((($s+1)*$m4)-(3*($s-1)*$m2*$m2));
+                    $k4= $s*$s*((($s+1)*$m4)-(3*($s-1)*$m2*$m2))/(($s-1)*($s-2)*($s-3));
                     if ($k2){
                         $quizstats->kurtosis = $k4 / ($k2*$k2);
                     }