//By: corozco@salud.gob.sv / cmartin@salud.gob.sv
//License: GNU/GPL v3 or later
<script type="text/javascript" charset="utf-8"> 
  $(document).ready(function(){
    // Initialy hiding all options of filtered question
    $('#question30 option').hide();
    // Just show the first option: "choose..."  
    $('#question30 option:eq(0)').show();
 
    // The trigger
    $('#question29').on('change',function() {
      var value = $(this).find(':selected').val();
      var start = 0;
      var end = 0;
 
      // Definition of limits
      switch (parseInt(value)) {
           case 1: 
             start = 1;
             end = 12;
          break;
        case 2:
          start = 13;
          end = 21;
          break;
        case 3:
          start = 22;
          end = 54;
          break;
        case 4:
          start = 55;
          end = 70;
          break;
        case 5:
          start = 71;
          end = 92;
          break;
        case 6:
          start = 93;
          end = 114;
          break;
        case 7:
          start = 115;
          end = 132;
          break;
        case 8:
          start = 133;
          end = 158;
          break;
        case 9:
          start = 159;
          end = 178;
          break;
        case 10:
          start = 179;
          end = 198;
          break;
        case 11:
          start = 199;
          end = 210;
          break;
        case 12:
          start = 211;
          end = 223;
          break;
        case 13:
          start = 224;
          end = 239;
          break;
        case 14:
          start = 240;
          end = 262;
          break;
        default:
          start = 0;
          end = 0;
        break;
      }
      //alert(value+' '+start+' '+end);
 
      //loop for hiding from the first drop-down item until the first showed
      for(i=1; i < start; i++) {
        $('#question30 option:eq('+i+')').hide();
      }
 
      //loop for showing related items
      for(i=start; i <= end; i++) {
        $('#question30 option:eq('+i+')').show();
      }
 
      //loop for hiding from the last showed til the last option
      for(i=end+1; i <= 263; i++) {
        $('#question30 option:eq('+i+')').hide();
      }
    });
  });
</script>