Mental Illness Is Not Evidence Against Abuse Allegations

ETA: this post was pretty much refuted by comments below.

I've noticed a situation several times that I think deserves attention.

Somebody goes around saying they've been the victim of mistreatment. But they seem mentally ill. Whether or not you know of a diagnosis, they seem "off" somehow -- highly agitated, making social faux pas, telling stories that don't quite add up. So people are very suspicious about whether their allegations are true.

Is this rational?

In general, someone who seems less trustworthy should be believed less. And, yes, mentally ill people are more likely to be delusional or exaggerating. But they are also more likely to actually be victims of crimes than the general population.

40% of women in the UK with severe mental illness are victims of rape or attempted rape.

People with severe mental illness are 6x as likely as the general population to have recently experienced sexual violence.

30% of mentally ill adults in an American study had been victims of violent crime in the previous six months.

Mentally ill adults in Sweden are 5x more likely than the general population to be murdered.

More than 25% of severely mentally ill Americans have been the victims of a violent crime in the last year, 4x the rate of the general population.

30-33% of psychiatric patients have been victims of domestic violence.

Someone being mentally ill is evidence for, not against, their being victims of a crime. And the base rates of violent crime are pretty high, so all things being equal, "someone attacked me" is not an extraordinary claim. Even when someone seems crazy and has made a lot of claims you don't believe, it can be reasonable to believe their claims of crime victimization. Don't fall into the horns effect.

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The question isn't P(ever abused|mentally ill), the question is P(true accusation|mentally ill). Maybe 40% of mentally ill women have been victims of at least 1 attempted rape at some point in their lives, but if they go around making dozens of rape accusations, while non-mentally-ill women hardly ever do, then a mentally ill accuser is strong evidence that a specific accusation is probably false. None of the statistics you quote bear on this or prove your claim. (One might say you spend all your effort establishing a denominator but forget the numerator.)

Don't fall into the horns effect.

The horns effect is real because everything is correlated.

Thanks; I think I was just wrong here, I didn't think of that.

I think it might be good to update the title of the post with a [Edit: Updated] tag or something.

Might also be useful for the disclaimer you added to the top to include a more complete explanation of your current take on the situation (although maybe a bit more work, and depends on your what your actual current take is).

AFAICT, Ben's comment was a decent synthesis of the point you were originally intending to make and gwern's counterpoint. While I don't think the point as originally worded was correct, it was still pointing at a fact that I don't think most people really have fully integrated into their model, and that seemed like something important enough that just saying 'refuted' didn't quite seem right either.

Questions about priors:

Are you assessing that the rate of false accusations from an individual is correlated positively, negatively, or not at all with the rate of actual rapes experienced by those individuals?

Do you model the probability of an individual experiencing abuse as random, negatively correllated with prior abuse, or positively correllated with prior abuse?

Does adjusting these priors affect the assessment you made above?

Relevant: section three paragraph 7 on serial abuse victims. There's probably more to say, but I think that some combinations of answers to the above questions lend support to the OP.

Just looking at that first link, the methodology was apparently

They were interviewed using the British Crime Survey questionnaire for domestic and sexual violence, and their responses were compared to those from 22,606 respondents to the 2011/12 national crime survey.

I find it totally plausible that there's a much higher base rate of crime, abuse, etc among the mentally ill. But if we want to argue against the model "mentally ill people are more likely to be delusional or exaggerating", then a study which just asks them is not going to lend much evidence.

I think this post has helped me be less confused on this matter. In my life, I have been seriously mislead by people close to me with mental illness about traumas that they have faced - people who had experienced significant abuse, telling me that they experienced different abuses which they had not experienced.

I think previously I would've expressed it in a more confused way, that their being mentally ill was not evidence against their having experienced abuse. But I would now phrase it that both my prior on them having experienced severe trauma is higher, and also the standard of evidence I require to believe a particular instance of abuse is also higher.

I guess there's a desire that these two things would cancel out. One might hope to say that it doesn't take more effort to discover abuse in the life of a person with severe mental illness than otherwise, but I think that the truth is that it just does take more effort to help prevent any abuse in this situation. I'll phrase it this way: if I am taking care of / in a significant relationship with someone who is severely mentally ill, while I might not trust their direct reports as much, I will increase my prior that there is, and increase my desire for evidence for the lack-of, abuse in the various parts of their life.

This post may not have been quite correct Bayesianism (... though I don't think I see any false statements in its body?), but regardless there are one or more steel versions of it that are important to say, including:

  • persistent abuse can harm people in ways that make them more volatile, less careful, more likely to say things that are false in some details, etc.; this needs to be corrected for if you want to reach accurate beliefs about what's happened to someone
  • arguments are soldiers; if there are legitimate reasons (that people are responding to) to argue against someone or see them as dangerous, this is likely to bleed over to dismissing other things they say more than is justified, especially if there are other motivations to do so
  • the intelligent social web makes some people both more likely to be abused, and less likely to be believed
    • whether someone seems "off" depends to some extent on how the social web wants them to be perceived, independent of what they're doing
    • seriously I don't know how to communicate using words just how powerful (I claim) this class of effects is
  • there are all kinds of reasons that not believing claims about abuse is often just really convenient; this sounds obvious but I don't see people accounting for it well; this motivation will take advantage of whatever rationalizations it can

Charities that work with victims of torture rarely put actual victims in front of cameras to try to drive donations, as they're rarely sympathetic, in large part due to visible mental and physical consequences of the abuse they suffered. Adults who were victims of severe and prolonged child abuse are a good example of this as well.

Additional datapoint, researchers studying 'ability to read emotions in faces' found that incarcerated serial rapists were on average the best at it, and victims of sexual assault were among the worst. If I remember correctly, the paper contained a categorical refusal to speculate further about a predator-prey dynamic.

I expect much of these effects comes from mentally ill people being in worse circumstances, and disappears if you condition on circumstances, which it seems like you can usually do in practice.

I think that this analysis would benefit greatly from distinguishing between different types of mental illness. Mental illnesses can be vastly different. After all, the only thing in common between them is that they are mental conditions that are considered "not normal" for some definition of "normal". I suspect that different illnesses might have very different values of

  • The rate of being targeted by abusers.
  • The rate of reporting abuse which did not really happen.
  • The rate of not reporting abuse which did happen.
  • The credibility that other people lend to reports by such a person (possibly for irrational reasons).

I don't think "people with mental illness are more likely to say in surveys that they are victim of crimes" should lead one to conclude "if someone with a mental illness tells me that they are a victim of a crime, I should believe them even if there story seems fishy".

The first empiric data towards which you point has that quality and I haven't checked it for the other links. What Korzybski called consciousness of abstraction is important when making arguments like this.

Can you clarify which claim you are making? Is it this:

Somebody goes around saying they’ve been the victim of mistreatment. But they seem mentally ill.

people are very suspicious about whether their allegations are true.

Someone being mentally ill is evidence for, not against, their being victims of a crime.


they are more likely to actually be victims of crimes.


they seem “off” somehow—highly agitated, making social faux pas, telling stories that don’t quite add up.

For no reason.

I don't think they are more or less likely to be telling the truth. I'd be more inclined to propose that the mental health makes for a higher hurdle to be taken seriously because people may be thinking, "how am I supposed to help this person?" which is a hard question to answer for a not-mentally-unwell person.

This seems well into 'Politics is the Mind Killer' territory.

this isn't obvious to me, can you elaborate?

It definitely overlaps with politically-charged topics of how "society" treats various subgroups. I'm not sure I'd have gone so far as to call it mind-killing as written, but it could be taken that way (and I'll admit that I did initially take it badly, and gave it more thought primarily because of trust built from the author's previous posts).

As gwern pointed out, this post commits one of the basic fallacies of conditional probability. Since this is a somewhat politically charged topic, and sarahconstantin has been around a while and so could be expected not to make such 101-level mistakes under normal circumstances, someone could reasonably surmise that she stopped looking for possible counterarguments once she had reached a conclusion she liked for political reasons.