By CBS3 Staff

PHILADELPHIA (CBS) — A new study calculates the risk and severity of developing a degenerative brain disease associated with playing football. The risk of developing CTE increased by 30% for each year of football played, according to data published in the Annals of Neurology.

The risk for the worst forms of the disease doubled for every 5.3 years played.

The research was based on studying the donated brains of 266 former amateur and professional players.