Or that people likely to become criminals are more likely to to get themselves injured which the poster I was responding to thinks could be the cause of the correlation.
Seems like an opportunity for careful experimental design. I mean, you could easily make the case that people who are greater risk takers and more aggressive are both going to be more likely to be criminals as well as get head injuries. The devil is in the details of figuring out that relationship via experimentation.
Ok. So this study’s idea of careful experimental design was to use a control group of people who had had lower limb injuries but no head injuries. If that is not good enough to control for risk taking and aggression, what would a careful experimental design look like?
I’m not so much advocating for the current study, as saying, “Hey! reminds me of this thing I read a long time ago, that I wish I could find again.”
It wasn’t the one posted earlier: it wasn’t in The New Yorker; it was in something like Discover, or Scientific American. Some kind of serious science, but written for general readership-- not a professional journal.
You can’t diagnose it in living people, but autopsy clearly shows characteristic brain damage from CTE, and it’s not at all subtle. They showed us pictures of a normal brain, a CTE brain, and an Alzheimer’s brain, and it didn’t take any training to see that they were strikingly different.
So there’s definitely a thing that can happen.
The problem I’m having is that if you were abused as a child, you probably have a higher probability of both aggressive behavior and head injury, so how do you identify head injury as a casual factor independent from the psychological, physical and other neurological effects of abuse? The effects of abuse on a child are pervasive even in the absence of a head injury. In fact, I think it’s likely that even without a head injury, abused kids have a higher likelihood of aggressive behavior. But that’s what we have to prove, right? We have to compare the population of abused kids with a head injury to the population of abused kids without one, to kids that aren’t abused at all, and see what their relative levels of aggression are.
But even then we have a problem! Because if your abuse resulted in a head injury, it was probably more severe than that suffered by kids who didn’t have one. (But maybe not! Because you can get a TBI just from getting slapped around a lot. It’s a puzzle.)
My parents didn’t abuse me, but once my father accidentally caused me to fall from my full height so that I struck my forehead against a concrete floor when I was 6. When I was 11, a rock estimated at 2 kg of mass was thrown high in the air by a kid who couldn’t see me and it described a parabolic arc accidentally directly impacting my forehead. I got stitches there. Lucky the rock missed my glasses. Good thing I inherited a hard skull from my Irish ancestors. Also note that the center of the frontal bone, where I got my impacts, is a robust area of the skull that can withstand impact better than the sides.
I’m nonviolent to the point of being vegetarian. I drive at the speed limit and signal every lane change. I am the singular of anecdote, so take that for what it’s worth.
So you’re Johanna Anecdata. Not quite as catchy as Hannah Montana, but it’ll do. 
I’ve been knocked unconscious five times by various blows to the head. I’ve never been arrested for violent behavior, nor am I prone to it in the least.
Not all men are sex offenders, but most sex offenders are men.
In fact, the vast majority of men aren’t sex offenders, and also, the vast majority of sex offenders are men.
Conditional (Bayesian) probability has always been a tricky topic for laypeople.
There’s a specific brain disorder that is caused by repeated blows to the head.
Chonic Traumatic Encephalopathy, or CTE
It was first described in the medical literature in a clown, whose act was to be shot out of a canon. It’s fairly common in boxers, and was initially named for boxers, before getting the bland name it has today. It can be definitively diagnosed after death, via autopsy. Like Alzheimer’s disease, there’s no way to diagnose it for sure in a living person.
It is characterized by misfolded tau proteins, and it develops similarly to mad cow disease, in that once the misfolding gets started, it can progress on its own, without further head trauma. Blows that stretch the spinal cord (as the brain bounces around) were suspected as causal, at least in one presentation i went to.
It’s a real, well-defined disorder, but one whose prevalence is unknown. It’s mostly observed in athletes who suffer repeated blows to the head, from boxers to soccer players. It can cause violent impulses. (And other neurological problems, like poor memory and clumsiness.)
I’m guessing this is the hypothetical link between being abused as a child and abusing your children. But surely learned behavior (with a normal brain) is also part of the story.
I think the ultimate conclusion in the first article I read back in the 90s was that “more research was needed.” But not as a cop-out-- as a genuine conclusion-- something is going on, and in bears scrutiny. My gosh, how I want to find that article. The new one is just a springboard to talking about the old one.
There remain controversies in diagnosing CTE, as there’s overlap with other neurodegenerative conditions, arguments over histopathologic features at autopsies and a paucity of data about incidence in the general population and correlation with clinical features.
http://academic.oup.com/braincomms/article/6/2/fcad314/7614163
It’s not the slam-dunk diagnosis news and sports media often make it out to be.
How much phosphorylated tau protein makes a violent abuser or killer?
Which is another thing that you could rule out by using people with other injuries as the control group, because people can be given opiates for any sort of painful injury.
You look at other people who have similar head injuries, but from non-abusive causes.
I know a lot of people who smoke cigarettes and don’t have lung cancer, but that doesn’t mean that smoking doesn’t cause lung cancer.
True, but it also means that you can’t assume that everyone who develops lung cancer smoked.
The guy in the original study was looking for a way to either help or reassure people who had been abused in regard to not abusing their own children.
Is it too far-fetched to say to people who were never head-injured that they will be OK, but taking a parenting class never hurt anyone, and to people who were head-injured, that they definitely should take parenting classes, and either remain in therapy while their children were at home-- or at least while they were young, if the parent was doing well, or join a 12-step group for abusive parents and people who did not want to become such?
That doesn’t follow logically. It is likely that you only develop mesothelioma if you have been exposed to asbestos or a small number of similar minerals. It’s also true that most people exposed to those minerals never develop mesothelioma. But essentially no one develops meso without exposure to those minerals.