Brain damage found in 110 of 111 deceased NFL players: study

Because the brains studied were for the most part donated by concerned families, they do not necessarily represent all people who have played the rough contact sport.

That's an important note: these 111 deceased NFL players are "pre-selected," not a random sample (the families who donated bodies for the study already had suspicions that their NFL player likely had CTE)

So it doesn't mean that 99% of all NFL players have CTE

Still, it also doesn't mean that this finding isn't significant - it further establishes what we already know, that repeated head trauma leads to CTE, and that a significant portion of NFL players will end up with it (how much portion we won't know unless there's a random sample study)