Elegant Point wrote:

The hypothesis is rejected   (notes Cilic is just outside the top 30 and n=1)

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 Hi elegant point, 

Unfortunately no hypothesis is able to be rejected by this, even you yourself must be aware of comparing two vastly different scenarios to prove your point? Davis Cup/Olympics vs ATP 500. 

Vast differences being playing for one's country which obviously is very important for all players, a match (for example Djokovic chooses if he wishes to play more than the captain) with a known friend/colleague who they might have played together with several times before, it being the crucial match to win the tie etc etc. As we saw with Rafa in Davis Cup or Novak in ATP cup final where him and Victor beat (two singles players) a decent level doubles team. 

Comparing to a second or third round in an ATP 500 where if the players weren't put together by the tournament, they either haven't played that much together to date, or it proved the logical thing to be able to enter the doubles draws due to only select number of places being available. I personally don't see Cilic and Novak as the ideal doubles pairing (maybe they're good friends, Croatians and Serbians are often close; Novak and Goran for example) but it was an outing people maybe got to see the top 2 singles players playing a match they might not of been able to see otherwise, so everything good.

Do the singles players have to play the doubles event? No. Are they the first ones to withdraw from it due to tiredness and unwillingness to play if they deem it appropriate: yes. I seem to remember Novak playing doubles event in this same tournament about 4 or so years ago where he played with his brother Marco who was about 400 ATP at the time, would you believe this to of happen with any other ATP 400 player, or was because of his surname? would you believe this to have been a Davis cup final worthy match? If so, much like next week where someone posted the doubles pairings, a lot of them look very much like they were put together by the organisation (except maybe Karen and Rublev), why are a lot of the singles players playing doubles next week as well: money, not likely looking to win the whole tournament considering they are singles players and there for the singles event while doubles is obviously very interesting without this input of the singles players draws would be smaller and prize money would lower, so benefit for all really. I expect the LTA is probably singing how Salisbury beat Novak etc etc and that's something Joe (I think its Joe no?) will always be able to say he did, but under what conditions?

Either way I reject your rejection of the null hypothesis