I'm not sure about that, but I doubt it.
Originally Posted by benbob
I don't think so, but an old doctype signals that the site may be built with outdated coding practices, such as tables for layout, which I do believe affects Google ranking a bit. It would be worth switching to a strict doctype and see what errors you get then. That would be very instructive.
Is there a practical reason like better serp ranking?
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<meta http-equiv="content-type" content="text/html; charset=utf-8">