MDL-16952 "after DB field type changes standard deviation and facility index show up as 0% instead of blank" Problem is that question->maxgrade is now 0.0000 and not 0 and $maxgrade now does not evaluate as false, need to use $maxgade!=0 which evaluates as before.

mod/quiz/report/statistics/qstats.php

@@ -135,7 +135,7 @@ class qstats{
 
     function _initial_question_walker(&$stats){
         $stats->gradeaverage = $stats->totalgrades / $stats->s;
-        if ($stats->maxgrade){
+        if ($stats->maxgrade!=0){
             $stats->facility = $stats->gradeaverage / $stats->maxgrade;
         } else {
             $stats->facility = null;

mod/quiz/report/statistics/statistics_table.php

@@ -171,7 +171,7 @@ class quiz_report_statistics_table extends flexible_table {
     }
     
     function col_sd($question){
-        if (!is_null($question->_stats->sd) && $question->_stats->maxgrade){
+        if (!is_null($question->_stats->sd) && ($question->_stats->maxgrade!=0)){
             return number_format($question->_stats->sd*100 / $question->_stats->maxgrade, 2).'%';
         } else {
             return '';