SetTimeout of recursive call without quotes error

Using setTimeout() to make recursive calls, if the first argument is not quoted, firefox prompts setTimeout():uselesssetTimeout call (missing quotes around arguments ?) If it's in quotes, firefox will prompt that function undefined

function refreshNum() { 
$.ajax({ 
type: "POST", 
url: "ajax/RefreshNum.ashx", 
async: false, 
data: {}, 
success: function (data) { 
varnumArry = data.split(','); 
$.each($(".rush_left"), function (n) { 
$(this).children().eq(0).html(numArry[n]); 
}); 
setTimeout(function () { refreshNum(); }, 3000); 
//setTimeout("refreshNum",3000); // It's going to make a mistake ,setTimeout() The first argument to a function must not be a simple function call, but an anonymous function! Why not  
} 
}); 

} 
refreshNum();