var myTextExtraction = function(node)
{
    // extract data from markup and return it
    t = $(node).text();
    return t.toLowerCase();
};

$(document).ready(function(){
  $(function() {
    $(".jquery-tablesorter").tablesorter(
      {sortList: [[3,1]],
       cssAsc: 'jquery-tablesorter-thUp',
       cssDesc: 'jquery-tablesorter-thDown',
       cssHeader: 'jquery-tablesorter-th',
       textExtraction: myTextExtraction
       }
    );
  });
});