People kept telling me "no news is good news," but it was only a couple of weeks ago that I had it explained to me exactly what that means.
Most schools review applications on a continuous basis. When they get to your file, they will review it (with however many people they use to review) and then either mark it "invite for interview," "hold," or "reject." Each time through, more people are weeded out from either end (i.e. they're either invited to interview or they're rejected). If you haven't been rejected yet it means you're in that group in the middle which is continuously shrinking...which means you're being compared to a smaller and smaller number of people each time. Plus, more of the really strong candidates are being removed each time through, so you're not competing with as many of those folks.
Of course, you're not competing with as many of the really weak candidates, either--and each time through, more interview slots are filled. So it's not an entirely positive thing...but rest assured, as long as you haven't gotten a rejection, you're still very much in the running!
