A lot of work was done here by
JPF,
Ocean and
Red Edhttp://forum.enjoysudoku.com/viewtopic.php?t=4771&postdays=0&postorder=asc&start=30EDIT
From this I take it that if you reduce a solution grid to
43 clues ~ 50 % will be valid, [none will be minimal]
Generating minimal puzzles from a full grid - is relativly easy to get 22-28 clue minimal puzzles. Its difficult to produce a minimal puzzle with >28 clues !
Generating puzzles from other minimal puzzles with the same number of clues will give both minimal and non-minimal puzzles.
from making 20s-19s-18s-17s
10% of 20s are non minimal
5% of 19s are non-minimal
1% of 18s are non-minimal
taking a 24 clue minimal puzzle and making many others - 75% of these were non-minimal
30 clues - 99.9 % non-minimal
StrmCkr wrote:100% at 39 clues. {chance to find this is slim}.
"slim" should read "extremely slim" [ approx 1 in 10^30 perhaps]
C