function displayByYear() {
	Event.observe('go_btn', 'click', showHide, false);
}
			
function showHide() {
	var x = document.display_years.select_years;
	var year = x.options[x.selectedIndex].value;
	for (i=1;i<x.options.length;i++)
		$(x.options[i].value).style.display = (year=="") ? "" : "none";
	if (year) $(year).style.display = ""; 
}