clear selected option in choice field

Hi,I want to clear a selected option in a choice field. I can set the field with the code below in JavaScript.

NWF$('#' + appplicationUsedID).find('input:radio[value="Yes we still use this application"]').attr("checked","true");

I tried clearing the field with the javascript below but setting it to false but this doesn't work.

NWF$('#' + appplicationUsedID).find('input:radio[value="Yes we still use this application"]').attr("checked","false");

Any help appreciated.

Cheers

Ian