Going back to my question, we don't have a lot of foreigners on this site no? Just surprised. I grew up in a war torn country and I can't remember anyone talking about concussion.

Regarding the maths. It is a rough estimate based on the flow of concussions. You are right I might be underestimating the flow because the number I use is only those who show up for care. Also I use the greek study of 0.9% symptoms beyond 1 year and made the assumption that symptoms are resolved within 4 years. I understand that this is not the case. That the distribution is right-skewed.

Here is an estimate based on the stock rather than the flow, focused on long term disability. The stock is estimated back in 2006 to be 5 million.
http://www.nacmed.com/uploads/1/4/1/...ain_injury.pdf

Clearly it could have grown since. Now PCS is only a portion of TBI (which includes moderate and severe TBIs). I have no idea. Out of total TBIs in a given year I am Concussion is around 75% (researched). But when you look at long term disability, the share of concussion must be much smaller since only a very small share last longer than a year. Assuming all moderate and severe TBIs lead to disability, there are about 1 million cases every 3 years, so the share of PCS in that 5 million pool cannot be very large...

My point is that if you are living with PCS beyond 1+year you are a part of a very small population that is very likely less than 1% of population...