It is self reported, so you have to take the data with a healthy dose of skepticism, but it is the only publicly available information on cross admits that I am aware of. My general feeling is that if it is statistically significant (the cross admit data is color coded in red and green for the 95% confidence interval), then it might be directionally correct. So do 65% of cross admits choose Penn over Brown? Who knows, but directionally I think a majority of cross admits probably choose Penn over Brown.
Another issue is that it does not take into account that one of the schools you might compare might be an EA school and the other might be an ED school. That could completely skew the data