The denominator has no relevance to how selective your hiring process is. Your process does not become more exacting and precise simply because you received more applicants.
Thank you for confirming that you were using the colloquial version of "selectivity" which doesn't require knowing the denominator instead of mathematical "selectivity" which does.
That wiki page orders the ranking on mathematical selectivity and not colloquial selectivity. My previous comment of Google Inc being more "selective" than Harvard is to be interpreted as mathematical selectivity. Sorry for not stating it more explicitly to prevent confusion.
So you don't care about on what basis selection is performed?
If your assertion is just that Google rejects a higher proportion of applicants than Harvard, that's... not at all interesting. The lottery rejects and even larger proportion of applicants for its 'grant' program, but I'm not going to try to learn anything from how it goes about picking winners.
