10 to 15 percent 60 percent 10 to 15 percent half multiple sclerosis multiple sclerosis half 10 to 15 percent 10 to 15 percent 60 percent less than 15 percent half less than 15 percent multiple sclerosis 60 percent 60 percent less than 15 percent multiple sclerosis less than 15 percent multiple sclerosis half multiple sclerosis