The Bethe formula
An alternative to Neuberg, proposed by Henry Bethe, was discussed on BLML
http://osdir.com/ml/games.bridge.laws/200208/msg00829.html
The Bethe formula is:
P_{N} = (P_{n} − 50) · 
n − 1
n + 1

· 
N + 1
N − 1

+ 50 
 (1) 
If N > n the corrected percentages are in between those from Neuberg and the "manual method".
The assumption made by Bethe is:
One conceptually attractive
approach is to assume that the known group was drawn at random from the
larger group. Since they are randomly drawn, all possible distributions
within the larger set are equally likely. But the best guess is that the
smaller set was equally distributed throughout the larger set.
We will not discuss the merits of this method here.