Can data on this site tell us whether White vs Black has an advantage in different varieties? I've heard anecdotally that White has an advantage in International checkers but has a disadvantage in Frisian checkers.

Yes, for Frisian Draughts white is a disatvantage. The position is not worse, but black is way more flexible in the opening and usually can dictate what type of game the want to play (espacially after whites 1. 31-26)

In Frisian Draughts I tend to play more conservative with the white pieces, and push for agressive openings and gambits with black

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