Ajax.Request Return Value

Anyone know how to return true or false to an event handler based upon the results that come back from a Prototype Ajax.Request call?

I have a link with an onclick handler that calls a function getLoggedIn(), which looks like the following:

function getLoggedIn(type) {
ajax = new Ajax.Request(
'includes/checkloggedin.php',
{
method: 'get',
parameters:'&type='+type,
onComplete: checkLoginResult
});
}

As any analysis of request.responseText occurs in checkLoginResult(), not getLoggedIn(), how can I pass an Ajax-response-determined return value back to the event handler?