If ..else in php

In before record added I have inserted the below code.

The problem I'm having is that when I input a "no" in the field IsSubjectEntitydifferent, the field CommEntity receives the values of $entityyes, instead of $nothingnoted.

Something must be wrong in my syntax, but not sure what. Please assist if possible.
$nothingnoted="No comments applicable";

$entityyes = "The entity provided by the subject was ".$values['SubjectName1']."They have informed us that this is a different entity to the original requested entity ".$values['RequestedEntityName'];

$CtrlIsSubjectEntitydifferent= $value['IsSubjectEntitydifferent'];

if($CtrlIsSubjectEntitydifferent="yes"){

$values['CommEntity'] = $entityyes;

}else {

$values['CommEntity'] = $nothingnoted;

}