Un petit exemple vaut mieux qu'un grand discours :-)

var recognizePattern = 'autoselect-';
 
var inputCollection = document.getElementsByTagName('input');
var collectionLength = inputCollection.length;
 
for (var j = 0; j < collectionLength; j++) {
 
	var myInput = inputCollection[j];
 
	if (myInput.getAttribute('type') == 'checkbox' && myInput.getAttribute('id').indexOf(recognizePattern) == 0) {
 
		myInput.addEventListener('change', function() {
 
			var mySelect = document.getElementById('slt');
			var optLength = mySelect.options.length;
 
			var re = new RegExp(this.getAttribute('id').substr(recognizePattern.length));
 
			for (var i = 0; i < optLength; i++) {
 
				if (re.exec(mySelect.options[i].text)) {
 
					mySelect.options[i].selected = this.checked;
 
				}
 
			}
 
		}, false);
 
	}
 
}