And we don't know which way it self selects or if it's the same for all cars. Do people who own toyotas who have problems not send in the forms because they can't bear to admit their perfect car isn't perfect. Do people who own Taurus and who have had trouble make damn sure to return it to let everyone know that domestic cars suck?
It's OK if used wisely but can be way off the mark in many cases. The one thing they USED to do was include a measure of problems AND what it cost to fix them. That, of course, made some of their favorite cars start to look not so good since only one out of warranty "electric" problem on a Mercedes might cost 4 times what a single "electric problem" on a Cavalier might cost. So now a $4 repair on a Cavalier counts the same as a $400 repair on a Mercedes.
The other thing they do is order their cars stupidly. They will rave over the mediocre "good" handling of some little import and rant over the terrible handling of a Caprice (this example is from a few years ago now). But for $40 they could have ordered the handling package on the Caprice and it would have run the little import off the road. But they are too frigging stupid to do that. The little import, of course, doesn't even offer people the choice of bathtub vs police car handling.