I don't know if this has ever been studied carefully, but they've done so with aging football players, and the percentage is staggering. - And those guys wear helmets. (Of course, I'm referring to American football, not that sissy game they play in the rest of the world. )
i thought it was higher. i heard even sugar ray robinson had memory problems at the end as well as floyd patterson. but honestly i use to feel sorry for boxers and football players but at the end of the day they got a chance to do something very few people in life ever get to do. i don't mean fight, i mean a job that they love. not many people in life can say that they actually have a job that they love and look foward to going to everyday day. i think these people are blessed reguardless of the dangers of their vocation.
I've read it's more like 75%. Depends on the career in question and the threshold one considers to be count as damage. Clearly, many long-time fighters have problems.
I would think just about all of them suffer from it to one degree or another. Some cases obviously worse than others.
I think that's why a lot of fighters give themselves a time limit to be successful. "If I don't earn a title shot by 30 then I'm getting out" etc... If you're hugely successful you can justify the danger, if not, it's not worth it. I'd be interested to know what's more damaging, taking multiple knock outs or having never been knocked out but eating lots of lighter punches. My impression is quantity trumps quality in this case but who knows.
15-20%? We should be so lucky. I can only imagine the number's that low if they're using a very low number of minimum fights like 1 or 5 so a lot of weekend warrior types who box once in a bingo hall for $20 get thrown in with the rest of the sample.