I haven't seen any studies putting the prevalence of father-daughter incest as low as 0.6%. I believe that a quick google scholar search will lead you to guesst

I haven't seen any studies putting the prevalence of father-daughter incest as low as 0.6%. I believe that a quick google scholar search will lead you to guesstimate a figure about 10x higher than that (at the low end) but it depends on how the populations have been sampled, what the definition of incest is, and how surveys are worded. But in any case, sounds like GP is saying that the difference in prevalence of incest between boys and girls could lead to a difference of 0.6% in divorce rates. Which is quite a different hypothesis.