Fuchsia isn't my real name, alas. I swiped it from Gormenghast
I have no idea where the studies were published (so pretty unsubstantiated evidence from me). Try the student BMJ or just the BMJ in general as they tend to have information on this type of thing.
Interviews are notoriously unreliable. You cannot possibly judge if someone 'will be a good doctor' just from an interview. I agree that personal statement isn't good enough on its own - however neither is interview and both can prove inaccurate. Use both together by all means, but as both are pretty inaccurate, I doubt it will actually improve the 'accuracy', if you like, of finding 'suitable' applicants. How do you know how much weighting to give to one over the other? Maybe someone's been coached in their personal statement...but then again what if they've been coached in their interview?
Obviously anecdotal evidence is pretty useless, however just to be annoying

I will give an example; two friends of mine, whom I have known well for about 7 years (and I would say 7 years of knowing someone beats a 15 minute interview just by a little); one is very caring, kind, intelligent, brilliant in her academic work, loads of outside interests blah blah blah - would make excellent doctor - however, she is very patient and gentle and when challenged doesn't enjoying arguing. So in an interview situation, when challenged, she prefers to keep quiet - she's just that kind of shy, gentle person. The other friend - not academically anything special, but has the gift of the gab and can blab her way through anything. Second friend is accepted to medical school X, first friend not, on basis of interview. Fair? No. But that's how life is. Interviews are no more accurate than anything else but everyone seems to think that in 15 minutes they can peer to the depths of someone's personality and dredge out all their potential. Not so.