A new study found the brains of 87 out of 91 deceased ex-NFL players tested showed signs of a degenerative brain disease associated with concussions. After expanding their search to football players who played in high school, college, or semi-professionally as well, researchers with the Department of Veterans Affairs and Boston University still found signs of chronic traumatic encephalopathy in 131 out of 165 samples tested. Researchers concede the sample may have been skewed because many of the football players who donated their brains had previously suspected that they had CTE, which can only be diagnosed posthumously. But the study adds to a growing body of work suggesting a decisive link between football and the condition.