Почему ajax срабатывает сразу два раза?

echo "<td> 
<select id='ocenka-day".$chislo."-" . $rowstudentlist['id'] . "'> 
<option disabled selected></option> 
<option value='0'>Н</option> 
<option value='2'>2</option> 
<option value='3'>3</option> 
<option value='4'>4</option> 
<option value='5'>5</option> 
</select> 
<script type='text/javascript' > 
  $( document ).ready(function() { 
        $('#ocenka-day".$chislo."-".$rowstudentlist['id']."').change(function(){ 
        var value = $(this).val(); 
         var vstudiin = '".$rowstudentlist['iin']."'; 
         var vday = ".$chislo."; 
         var vprepodiin = '".$iin."'; 
         var vdisid = $selectdis; 
         var vmonth = $selectmonth; 
         var vgr = $selectgr; 
         var vsemestr = $semestr; 
      $.ajax({type:'POST', 
      url:'my-journals-save.php', 
      data:{ocenka:value,day:vday,studiin:vstudiin,prepodiin:vprepodiin,disid:vdisid,month:vmonth,gr:vgr,semestr:vsemestr}, 
      dataType:'html', 
      success:function(){ 
            } 
      });});}); 
  </script> 
</td>";