[Martee]

I think it's the DEGREE of open or closed clubface in relation to the plane line that determines how much hook or fade.

Annikan . . .

Excellent post...

As for scientific evidence, there seems to very little that addresses this issue in english.

Most noted instructors that I have come across that use the Ball Flight Laws really use it at a very coarse level and on full swings, no putters.

I long ago gave up on these discussions since there are two camps for sure and none can account for all the variables, the loft, speed, directional vectors, etc.