From: jamiesensei <jamiesensei>
Date: Tue, 21 Oct 2008 09:25:02 +0000 (+0000)
Subject: MDL-16951 "kurtosis and skewness equations were wrong" See changes to equations here... 
X-Git-Url: http://git.mjollnir.org/gw?a=commitdiff_plain;h=67710da492605fb7db4924fbd12924d8ac568a6d;p=moodle.git

MDL-16951 "kurtosis and skewness equations were wrong" See changes to equations here : http://docs.moodle.org/en/index.php?title=Development%3AQuiz_item_analysis_calculations&diff=45585&oldid=39752
---

diff --git a/mod/quiz/report/statistics/report.php b/mod/quiz/report/statistics/report.php
index cb70bb9117..c5413f2b87 100644
--- 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);
                     }