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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

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jamiesensei 2008-10-21 09:25:02 +00:00
parent 03043a3313
commit 67710da492
1 changed files with 2 additions and 2 deletions
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mod/quiz/report/statistics/report.php
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@ -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);
}