// add event listeners to event type checkboxes
	function initEventTypeCheckboxes(){
	
		if (!document.getElementById('event_type_checkboxes')) {
			return;
		}
	
		var event_type_checkboxes = document.getElementById('event_type_checkboxes').getElementsByTagName('input');
		
		// uncheck the all checkbox when an event type checkbox is clicked
		var num_checkboxes = event_type_checkboxes.length;
		for(var i=0; i<num_checkboxes; i++){
			event_type_checkboxes[i].onclick = unCheckAllCheckbox;
		}
		
		// Check all checkboxes when all is selected 
		var all_events_checkbox = document.getElementById('all_events');
		all_events_checkbox.onclick = checkAllEventTypes;
	}
	
	
	// want checkboxes to uncheck the all checkbox when clicked
	function unCheckAllCheckbox() {
		var all_events_checkbox = document.getElementById('all_events');		
		
		if(all_events_checkbox.checked) {
			all_events_checkbox.checked = false;		
		}
	}
	
	
	// Want to check all checkboxes when all checkbox is clicked
	function checkAllEventTypes(){
	
		if (!document.getElementById('event_type_checkboxes')) {
			return;
		}
	
		var event_type_checkboxes_container = document.getElementById('event_type_checkboxes');
		var event_type_checkboxes = event_type_checkboxes_container.getElementsByTagName('input');
		
		var all_events_checkbox = document.getElementById('all_events');
		if (all_events_checkbox.checked) {
			var num_boxes = event_type_checkboxes.length;
			
			for (var i=0; i<num_boxes; i++) {
				event_type_checkboxes[i].checked = true;
			}
		}
	}