What percentage of those who do those 60 mile three day walks actually go the distance in the time allotted?

They have two annual walks here like that. One is 60 miles, the other is 59 (I wonder if anyone ever chooses the 59 because 60 is just way too far) for cancer research. I tried to look online, but nowhere does it say how many who start actually complete. I’d be sure it’s not 100% (I do an annual 4 miler where only about 95% complete). The over/under on this may even be as low as 50%, and since this is simply a fund raiser for participating, and not miles actual logged ($5.00 per mile walked pledged or whatever), I would bet that the motivation level to fully complete is lowered just a touch and I’d be flirting with taking the under on this. And for the record, this question is NOT about money, it’s about those charity walks.