clicked radio button value is displayed as undefined

clicked radio button value is displayed as undefined

The result is shown as undefined for the value of radio button being clicked
$(document).ready(function(){
$("input:radio").change(function(){
checkResult(this);
});
});
function checkResult(el)
{
var clicked=$('el:checked');
var clickedvalue=clicked.val();
alert(clickedvalue);
$this=$(el).parent("div.QA");
$this.slideUp();
}