I think that NTRP should be separate for singles and doubles. I am probably a half level (.25) better at singles than I am at doubles. Most of the players I know are middle-aged to elderly, and play mainly doubles since they aren't as fit anymore or never developed solid groundstrokes. I think there are people who have beaten me in doubles that I would probably bagel in singles. And I've seen people that have huge deficiencies in their game that don't get exploited because the doubles game does not allow as many opportunities for an opponent to do so. As long as singles players keep playing singles and doubles players keep playing doubles, the NTRP doesn't really matter. But if they switch back and forth, I would think their ratings (and those of people playing against them) can get all out of whack, and therefore they should be measured separately between singles and doubles. What are your takes?