After adjusting for the age and type of motorcycle, rider age, gender, marital status, weather and other factors, the actual increase was about 22 percent relative to a group of four comparative states, Illinois, Indiana, Ohio and Wisconsin, the study found. (Quote from the article)
Even if they did not factor for a given % of increase per year in health care cost (very doubtful), treatment costs increased.
I could personally care less if a person wears a helmet or not, but no logical argument can be made saying that IF you crash, and IF you hit your head in that crash, that you are not more likely to suffer more serious head injury without a helmet than with one. That is not to say that IF you are wearing a helmet you will NOT incur a head injury like a serious concussion, but in that same crash, with the same impact to the head, if you're NOT wearing a helmet, there is a MUCH higher probability that part of your skull will be fractured. Personally, I'd rather have a concussion than have them picking parts of my skull out of my brain, along with gravel or glass from my head going through a car window, or tree bark after impacting a tree on the side of the road.
However, in these kinds of studies, while percentages matter, the actual NUMBER of incidents are tiny compared to accidents involving other types of vehicles, like cars, trucks, etc.
BTW....health care costs from 2009-2011 rose at about 3.9%, compared to 6+% from 2000 through 2007. The recession played a part in that, along with other factors, but even just looking at health care unaffected by the recession, like Medicare costs, the rate of increase dropped. What will it do in the future? Only time will tell.