A Simple Question ...

[fishtownraider]

... or so it seems, but I can't seem to find a simple answer. I'm sure Peter will know, though. It is this: in what proportion of professional football matches is at least one goal scored in the second half? I can find plenty of sites telling me what % of goals are scored in the second half, but that's not the same thing. (Pointers to any filtering, e.g. by country or league, would also be helpful.) Thank you.