Studies on PTSD

How gender, genes, and disorders relate to PTSD

This study randomly selected 1,000 people in their 20s for a health study and followed up with them 10 years later. They found that half of them had experienced traumatic events that are known to cause PTSD and 5% of them actually developed PTSD. The most common of those traumatic events were

…physical assault, severe injury or accident, witnessing violence, and a family member or a close friend severely injured or killed.

Females were slightly less likely to be exposed to traumatic events and were twice as likely to develop PTSD. This study found the same thing. And this one too.

Higher female likelihood of PTSD makes sense when you consider sexual assault had the highest likelihood of resulting in PTSD (16.5%) and women have higher neuroticism than men (a personality trait which is associated with PTSD. see here here and here).

This study looked at gender differences in PTSD after only car accidents so it should indicate whether the gender difference is caused by the kind of people vs. the kinds of trauma because it’s the same kind of trauma in all instances (car accident). It found that women were several times more likely to experience many PTSD symptoms. It’s worth mentioning that the sample size was only 122.

This study (2006) randomly selected 823 6-year-old children and were able to follow up with 713 of them 11 years later. 76% of them had experienced an event known to cause PTSD. Of those, 8.3% of them actually had PTSD.

So the first study looked at people in their 20s and the one directly above looked at ages 6-17, and they both found that more than half of their subjects had experienced trauma. It’s pretty unlikely that you’ll get to 30 without experiencing at least one traumatic event known to cause PTSD, and you’ll probably endure multiple of them.

High IQ (115+) correlated with both a lower likelihood of experiencing a traumatic event and a lower likelihood of getting PTSD if a traumatic event was experienced. Females were twice as likely to experience PTSD even though they were slightly less likely to experience a traumatic event (same as the studies above). The tendency to externalize problems (as rated by teachers) was associated with PTSD. The really big one is growing up in an urban household. Because they tended to live in urban settings, single mothers and children of low birth rates also had a high likelihood of getting PTSD.

The most commonly experienced traumatic event was, “learning of a sudden unexpected death of a close friend or relative”, which is something we’ll all eventually experience.

Why are some populations are more vulnerable to PTSD than others?

As previously mentioned, 76% of kids age 6-17 experienced trauma, 50% of people in their 20s experienced trauma. This seems like a lot but not all traumas are equal. Being shot/stabbed or raped is on a whole other level as someone who learned of a sudden unexpected death or learned of trauma to others. Also, some people experience trauma recurrently (think childhood abuse), and others experienced one event (mugged).

Several variables like high IQ or low neuroticism make one less likely to experience PTSD after trauma. One way to interpret that is as some kind of inherent immunity. Several studies make this inference outright.

“High IQ protected exposed persons from succumbing to PTSD.”

The inherent immunity hypothesis is probably right, but there are other possibilities. There’s no attempt to account for kinds and frequencies of traumatic events. We already know non-high IQ people are more likely to experience traumatic events in the first place, and that’s easy enough to control for, but isn’t it likely that non-high IQ people are also exposed to repeated and more severe traumatic events like assault, child abuse, and rape?

If we compared the kinds and frequency of traumas, the advantage some kinds of people have might go away.

They can’t possibly compare similar kinds of trauma without much larger sample sizes. 713 people, 541 cases of trauma, and 45 cases of PTSD couldn’t possibly get there. That’s fine. Researchers have data limitations. But that means they acknowledge possibilities then make no inference at all rather than make the wrong inference from a limited dataset.

There’s no resource better than this paper for learning about the history of changing PTSD criteria. The diagnostic and statistical manual (DSM) was updated several times to broaden the definition of PTSD since 1952 (and then contract the definition since 2013). Over the last 40 years it went from only including instances as severe as the archtypical veteran experiencing flashbacks of war to something 1/9 women and 1/20 men will eventually have (“one of the most common mental disorders” 8% lifetime risk)

The first two manuals in 1952 and 1968 didn’t include the phrase Post Traumatic Stress Disorder but they referred to “a transient response” to “severe physical demands or extreme emotional stress such as in combat or in civilian catastrophe (fire, earthquake, explosion, etc.)”

The name PTSD came from the DSM-III in 1980. Since then the number of symptoms grew from 12 to 20.

The general trend since 1980 has been to broaden the definition, but it has both expanded and contracted in several specific ways, and since 2013 it has generally contracted. The number of criteria that must be met for symptoms grew from 4 to 6. They also changed the definition of trauma to omit instances of loved ones dying in non-violent deaths. Changes like these make it harder to get diagnosed with PTSD.

This study finds,

“that 25% of lifetime DSM-IV PTSD failed to meet DSM-5 criteria, and 12% of DSM-5 PTSD did not meet DSM-IV criteria, with a significant reduction in prevalence from 9.8% in DSM-IV to 8.3% in DSM-5. Sixty percent of DSM-IV diagnoses not meeting DSM-5 criteria were attributable solely to the removal of qualifying indirect exposures through trauma to loved ones involving nonviolent deaths.”

Is PTSD genetically inherited? Yes.

The variance in estimates of genetic influence is large. Studies report genetic influence between 24% to 72% following trauma. This makes sense if you consider some studies look at exclusively female twin pairs, and other studies look at exclusively male combat exposure veterans.

All of the studies I found showed zero non-shared environmental effects.

PTSD also overlaps with other mental disorders that we know have significant genetic components:

We found strong evidence of overlapping genetic risk between PTSD and schizophrenia along with more modest evidence of overlap with bipolar and major depressive disorder

Those with the inability to conjur mental imagery (aphantasia) may be more resistant to PTSD.

These data suggest the emotional response to reading fictitious scenarios is contingent on visual mental imagery. This is strong and novel evidence for imagery’s emotional amplifier role, underpinning imagery’s significant in disorders, such as PTSD, and their treatment.

This is only one study and it’s done on 46 participants, but the effect seems pretty significant

While control participant data monotonically rose (mean increase from baseline: 0.43 μS, SEM 0.11), the aphantasic SCL flatlined (0.07 μS, SEM 0.12)

Maybe the real reason this is persuasive is not because the study is so good, but because the conclusion makes so much sense if you just think about what PTSD and aphantasia are. It would be surprising if people with no mental imagery had a disorder that significantly depends on mental imagery.

How long does PTSD typically last? Can it be cured?

This meta-analysis looks at naturally occurring remission rates.

Remission was defined as the actual percentage of PTSD cases at baseline who are non-cases after a minimum of ten months. Forty-two studies with a total of 81,642 participants were included. The mean observation period was 40 months. Across all studies, an average of 44.0% of individuals with PTSD at baseline were non-cases at follow-up.

Those who endured natural disaster had the highest remission rates (60%). Those who endured physical diseases had much lower remission rates (31.4%).

This meta-analysis only looks at longitudinal studies and conveys a multitude of risk factors for longer-term PTSD periods.