Show:Hide a textfield after changing in dropdown list

Show:Hide a textfield after changing in dropdown list

I can't figure out why it dosen't work. I'd like to show/hide a <p> block depending on the value selected in the dropdown list:
$(document).ready(function(){
    $('#report_rep_type').change(function(){
      $('#report_rep_type').change(function(){
        if($(this).text()!= 'Contigency Liabilities/Others')
          $('#someElement').hide();
        else
          $('#someElement').show();
      });
    });
  });


HTML code:
<form action="my action>
<fieldset>
  <legend>Report details</legend>
  <p>
    <label for="report_rep_type">Report type</label><br />
    <select id="report_rep_type" name="report[rep_type]"><option value="">Please select</option>
<option value="Scientific &amp; Technical">Scientific &amp; Technical</option>
<option value="Financial">Financial</option>

<option value="Contigency Liabilities/Others">Contigency Liabilities/Others</option></select>
  </p>
  <p id="rpt_object">
    <label for="report_object">Object</label><br />
    <input id="report_object" name="report[object]" size="30" type="text" />
  </p>
  <p>
    <label for="report_frequency">Frequency</label><br />

    <select id="report_frequency" name="report[frequency]"><option value="">Please select</option>
<option value="3">quarterly</option>
<option value="6">half-yearly</option>
<option value="12">annually</option>
<option value="24">biannually</option></select>
  </p>
  <p>
    <label for="report_interval">Interval, weeks</label><br />

    <input id="report_interval" name="report[interval]" size="30" type="text" />
  </p>
  <p>
    <label for="report_alert1_interval">Alert 1 interval, weeks</label><br />
    <input id="report_alert1_interval" name="report[alert1_interval]" size="30" type="text" />
  </p>
  <p>
    <label for="report_alert2_interval">Alert 2 interval, weeks</label><br />

    <input id="report_alert2_interval" name="report[alert2_interval]" size="30" type="text" />
  </p>
  <p>
    <label for="report_formatted_end_date">Report end date</label><br />
    <input id="report_formatted_end_date" name="report[formatted_end_date]" size="10" type="text" />
  </p>
</fieldset>

  </p>

  <p>
    <button class="button " type="submit"><img alt="Tick" src="/images/silk/icons/tick.png?1245400388" /> Create</button>
  </p>
</form>


Any idea ? THank you