I dropped my sister on her head when she was a baby

Patient: When I was 11 years old and my baby sister was 6 months old, I was playing with her in the backyard. I dropped her and she landed on the back of her head. Since I was less than five feet tall and it was on a grassy lawn, I think it is unlikely that I did any damage. She didn’t cry much and she didn’t show any signs of being hurt at the time. I took her right into the house afterward and my mother never saw that anything was wrong. However, my sister, who is now in her 40s, tells people that I dropped her on her head and that is why she has attention deficit disorder. She also says that it is because of me that she could not do well in college and was not able to get a degree. She’s a smart woman in many ways, she was just never a great student. I, on the other hand, was a good student and graduated from college magna cum laude. I have attention deficit disorder, too. This may sound like a joke to you, but my sister is adamant about blaming me and she is very serious in her belief that I caused some brain damage. Will you tell me how likely it is that I caused brain damage to my sister?

Doctor: