HTML5 Canvas - Combobox clear values

I have tried in the following code:

$('#patients_cbx').prop('selectedIndex',0);

and also

$('#patients_cbx').val('');

I cannot find any reference from Adobe on doing this or a lot of other seemingly simple things...most frustrating!

		$.ajax({
			type: "POST",
			url: 'scripts/get_patients.php',
			dataType: 'json',
			data: {
				complexity: complexity
			},
			success: function (data) {
				$('#patients_cbx').prop('selectedIndex',0);
				console.log(complexity);
				for (var i = 0; i < data.length; i++) {
					$('#patients_cbx').append($("<option/>").attr("value", data[i].data).text(data[i].label));
				}
			}
		});