diff --git a/lib/models/LikertScale.php b/lib/models/LikertScale.php
index a4c0eb81ccc39e24e9c61cdff580b74c542cec56..4fde898fecefbc73a25f480ee8cb70905878db8c 100644
--- a/lib/models/LikertScale.php
+++ b/lib/models/LikertScale.php
@@ -74,7 +74,10 @@ class LikertScale extends QuestionnaireQuestion implements QuestionType
         [$statement_key, $options_key] = explode('_', $answer_option);
         foreach ($this->answers as $answer) {
             $answerData = $answer['answerdata']->getArrayCopy();
-            if ($answerData['answers'][$statement_key] == $options_key) {
+            if (
+                isset($answerData['answers'][$statement_key])
+                && $answerData['answers'][$statement_key] == $options_key
+            ) {
                 $user_ids[] = $answer['user_id'];
             }
         }
diff --git a/lib/models/RangeScale.php b/lib/models/RangeScale.php
index 66ea27da5d4631bb3407d6ada54fc4fe2de828b3..92c1fba91927adafc24926b6ed5821046caa0942 100644
--- a/lib/models/RangeScale.php
+++ b/lib/models/RangeScale.php
@@ -77,7 +77,10 @@ class RangeScale extends QuestionnaireQuestion implements QuestionType
         [$statement_key, $options_key] = explode('_', $answer_option);
         foreach ($this->answers as $answer) {
             $answerData = $answer['answerdata']->getArrayCopy();
-            if ($answerData['answers'][$statement_key] == $options_key) {
+            if (
+                isset($answerData['answers'][$statement_key])
+                && $answerData['answers'][$statement_key] == $options_key
+            ) {
                 $user_ids[] = $answer['user_id'];
             }
         }