Let's look at it from a wider perspective. Let's start looking at some of the things that make a head injury prediction complicated. CT's or MRI's are very good at picking up bleeding in the brain. At the same time, I have seen people with negative CT Scans and MRI's who are in a deep coma. This highlights the problem that medical tests are not always the best predictors of long-range outcome.
People bring different strengths and weaknesses to the recovery process.
One way of looking at differences in people is to look at their ability to solve problems. Psychologists use IQ tests to measure this ability. A 100 score is an average score. In general, having a higher IQ tends to help. However, there is a common problem that I have found with people who have a high IQ who get a head injury.