"Long-Term Outcomes Associated with Traumatic Brain Injury in Childhood and Adolescence: A Nationwide Swedish Cohort Study of a Wide Range of Medical and Social Outcomes", Sariaslan et al 2016, is a population registry study which reports within-family correlations adjust for education about various negative outcomes with 1 or more diagnosed TBIs representing 9.1% of the population (their twin sample was too small); within-family studies control for tons of the usual confounders (and indeed the correlations are smaller than if you had used the general population) and are probably close to the causal effect (possibly underestimating it since so many TBIs go unreported).

TBI is common enough that the effects are large on a population-wide basis:

We found that the crude population contributions of TBI explained approximately...2%–6% of the population differences in the outcomes. The strongest population attributable risks were found for the severe outcomes, including psychiatric inpatient hospitalisation (PAF = 5.5%; 4.9%–6.1%), premature mortality (PAF = 4.7%; 2.9%–6.5%), and disability pension (PAF = 4.6%; 3.8%–5.3%).

Interestingly, the effects of TBI get worse with age: the youngest age bracket (despite having lots of falls) has the smallest RRs while they increase especially for adolescents. (This was the opposite of what I expected.)

They find RRs of:

1. disability pension: 1.49

   • Population rate: 3.9%
   • Lifetime cost: Sariaslan gives a quick opportunity cost estimate of "US$1.3 million per person" from the inability to work & earn a normal income over the next 30 years

2. Psychiatric visit: 1.31

   • Population: 14.2%
   • Lifetime cost: ?

3. Psychiatric hospitalization: 1.57

   • Population: 5.7%
   • Lifetime cost: ?

4. Premature mortality (death age <41): 1.40

   • Population: 0.8%
   • Lifetime cost: tricky since it's not quite a RR on all-cause mortality: the age 41 is when they stopped following individuals in their sample. If we assume that the mortality RR remained indefinitely, then using my Gompertz curve functions, a RR of 1.40 for a 30yo would represent a loss of 3.09 years over the next ~50 years, for a 10yo a loss of 3.147 years over the next ~70 years etc. So ignoring discounting, ~\$150k from the mortality alone.

5. Highschool dropout: 1.28

   • Population: 8.9%
   • Lifetime cost: somewhere upwards of $250k in the USA, estimates as high as $1m.

6. On means-tested welfare benefits: 1.19

   • Population: 11.5%
   • Lifetime cost: Sweden is famous for spending a lot on welfare, but the welfare & public spending are quite diverse, this doesn't specify how long each individual is on welfare or whether it's household or individuals. http://ec.europa.eu/social/BlobServlet?docId=9044&langId=en suggests that a prevalence of 11.5% must refer to household welfare, and estimates that in 2008 the average number of months (from 1990 to 2008) was 6.1 months at 43987 SEK per month or \$5.2k or \$31.72k total on average.

So the undiscounted cost of 1 nonfatal TBI for a 10yo (why 10yo? so they have time to drop out of highschool) in Swedish America would be something like:

(0.039*1.49 -0.039)*1300000 + ? + ? (0.008*1.40 - 0.008)*3.147*50000 + (0.089*1.28 - 0.089)*250000 + (0.115*1.19 - 0.115)*31720 = >\$32,269

For the 30yo

(0.039*1.49 -0.039)*1300000 + ? + ? (0.008*1.40 - 0.008)*3.09*50000 + (0.115*1.19 - 0.115)*31720 = >\$26,030.482

Unfortunately, hard to see how to do much about this. The top category of TBI is normals falls, cars, then assaults, then miscellaneous: https://www.cdc.gov/traumaticbraininjury/pdf/blue_book.docx

An estimated average of 595,095 are fall-related TBIs, 292,202 motor vehicle traffic TBIs, 279,882 struck by or against events, and 169,625 assault-related TBIs occurred annually....Struck by or struck against events are those in which a person was struck unintentionally by another person or an object, such as falling debris or a ball in sports, or that someone struck against an object, such as a wall or another person. For this report, only unintentional and undetermined struck by or struck against events were included. Struck by or struck against events related to assaults (for example, being struck by a fist) are in the assault category. Struck by or struck against events were only reported for all ages because small sample sizes precluded reporting them for all three data sources (NHAMCS, NHDS and NVSS)

For 30yos, cars are 40% of TBIs, falls are 2.7% of TBIs, assault is 19% of TBIs, struck by by or against is 0.7%, and the ominous 'other' is 37%. So while we can probably ignore the 'assault' due simply to demographics (I suspect most readers here have low risk of crime), and car travel represents a fairly focused area of intervention, the 'other' can't be fixed except by always wearing a helmet, which would be difficult if only for social reasons.