diff --git a/question/bank/statistics/classes/helper.php b/question/bank/statistics/classes/helper.php
index b72f59bfd5e..c2845a54ba2 100644
--- a/question/bank/statistics/classes/helper.php
+++ b/question/bank/statistics/classes/helper.php
@@ -204,7 +204,10 @@ class helper {
      * @return array
      */
     public static function format_discrimination_index(?float $value): array {
-        if (is_null($value) || $value < self::NEED_FOR_REVISION_LOWER_THRESHOLD) {
+        if (is_null($value)) {
+            $content = get_string('emptyvalue', 'qbank_statistics');
+            $classes = '';
+        } else if ($value < self::NEED_FOR_REVISION_LOWER_THRESHOLD) {
             $content = get_string('verylikely', 'qbank_statistics');
             $classes = 'alert-danger';
         } else if ($value < self::NEED_FOR_REVISION_UPPER_THRESHOLD) {
diff --git a/question/bank/statistics/lang/en/qbank_statistics.php b/question/bank/statistics/lang/en/qbank_statistics.php
index 86ba58dfe17..3bf07d557fc 100644
--- a/question/bank/statistics/lang/en/qbank_statistics.php
+++ b/question/bank/statistics/lang/en/qbank_statistics.php
@@ -38,3 +38,4 @@ $string['verylikely'] = 'Very likely';
 $string['likely'] = 'Likely';
 $string['unlikely'] = 'Unlikely';
 $string['na'] = 'N/A';
+$string['emptyvalue'] = '-';
diff --git a/question/bank/statistics/version.php b/question/bank/statistics/version.php
index eee106f59e0..7e648afffb2 100644
--- a/question/bank/statistics/version.php
+++ b/question/bank/statistics/version.php
@@ -26,6 +26,6 @@
 defined('MOODLE_INTERNAL') || die();
 
 $plugin->component = 'qbank_statistics';
-$plugin->version   = 2021092000;
+$plugin->version   = 2021121500;
 $plugin->requires  = 2021052500;
 $plugin->maturity  = MATURITY_STABLE;