Eleven percent of people diagnosed with mood disorders such as depression and bipolar disorder are left-handed, says Jadon Webb. But among those with schizophrenia or schizoaffective disorder, a striking of 40 percent are left-handed. (Credit: Nate Steiner/Flickr)

Lefties more likely to have schizophrenia

People who are left-handed are more likely to develop psychotic disorders like schizophrenia rather than mood disorders such as depression, new research shows.

About 10 percent of the US population is left-handed. A new study that compares all patients with mental disorders, shows that 11 percent of those diagnosed with mood disorders such as depression and bipolar disorder are left-handed—which  is similar to the rate in the general population.

But “a striking of 40 percent of those with schizophrenia or schizoaffective disorder are left-handed,” says Jadon Webb, a child and adolescent psychiatry fellow at the Yale University Child Study Center, who has a particular interest in biomarkers of psychosis.

“In general, people with psychosis are those who have lost touch with reality in some way, through hallucinations, delusions, or false beliefs, and it is notable that this symptom constellation seems to correlate with being left-handed,” Webb says.

Tailored treatment

“Finding biomarkers such as this can hopefully enable us to identify and differentiate mental disorders earlier, and perhaps one day tailor treatment in more effective ways.”

For the study, published in the journal SAGE Open, Webb and colleagues studied 107 individuals from a public outpatient psychiatric clinic seeking treatment in an urban, low-income community.

The researchers determined the frequency of left-handedness within the group of patients identified with different types of mental disorders.

The study shows that white patients with psychotic illness are more likely to be left-handed than black patients. “Even after controlling for this, however, a large difference between psychotic and mood disorder patients remained,” Webb says.

Keep it simple

What sets this study apart from other handedness research is the simplicity of the questionnaire and analysis. Patients who were attending their usual check-ups at the mental health facility were simply asked “What hand do you write with?”

“This told us much of what we needed to know in a very simple, practical way,” Webb says. “Doing a simple analysis meant that there were no obstacles to participating and we had a very high participation rate of 97 percent.

“Patients dealing with serious symptoms of psychosis might have had a harder time participating in a more complicated set of questions or tests.

“By keeping the survey simple, we were able to get an accurate snapshot of a hard-to-study subgroup of mentally ill people—those who are often poverty-stricken with very poor family and community support.”

Source: Yale University

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11 Comments

  1. Joe J

    Actually, this study demonstrates a correlation between left-handedness and psychotic disorders. Given the small sample size, and the fact that all of the data came from one clinic means this could just be a statistical anomaly.

  2. Bryan

    A person’s dominant hand isn’t necessarily the one they write with. Before linking any disorders to left handed people, much more thought needs to go into how the study determines who is a lefty.

  3. Jonathan R

    Could it also be that a lot of people with mental disorders can barely write anything more than a cross so they don’t really care which hand they write with and are more likely to pick a handedness at random?

  4. JR Reply

    I encourage everyone to read at least the Discussion section (it’s an open access journal). No study is perfect, but I think this study provides good reason to attempt to replicate it.

    Joe J: The researchers point to recent evidence that patterns in hemisphere asymmetry may be involved in schizophrenia. It is a correlation, but it has been found in other studies (though methodology and results have been mixed). Do you have any plausible alternative explanations? We cannot experimentally manipulate handedness or schizophrenia.

    Bryan: Thought was put into the study. The researchers felt that some patients might not want to perform an extended assessment of their handedness (they discuss this in the Introduction). Their methods meant virtually all patients consented, increasing sample size and reducing sample bias. Again, past studies have addressed some of your concerns, with mixed results, but the overall picture is increased non-right-handedness in psychotic disorders (from short studies like this one to more extended ones done in the past).

    Jonathan R: You demonstrate a poor understanding of mental disorders. The authors refer specifically to psychotic disorders, not just any mental disorder. And, even with psychotic disorders, people are capable of making choices and writing, particularly with the help of antipsychotic medication. Your views are extremely stigmatizing–real people suffer these afflictions.

  5. Marc

    Wait, so we were right to punish people for being left handed? (I’m not serious, but I’m sure there will someone out there who will start a crusade against lefties sooner or later.)

  6. Derp

    This is terrible journalism and a complete misinterpretation of the statistics that the author herself gives within the body of the article. The headline is misleading, to put it mildly, and the first line of the article is just completely wrong. I don’t want to get into what kind of logical fallacy she made because that’s going to be hard to understand, so here is a hypothetical population to demonstrate why “People who are left-handed are more likely to develop psychotic disorders like schizophrenia rather than mood disorders such as depression” is an erroneous conclusion.

    Say there is a population of 100 people.
    30 are left handed, 70 are right handed.
    1 left handed schizo, 1 right handed schizo.
    10 left handed depressed people, 60 right handed depressed people.

    As you can see, 50% of schizos are lefties…. but only 14% of depressed people are lefties! The population of schizos have a much bigger proportion of left-handed people.

    But then you look at the whole picture and you can see that 33% of lefties are depressed while 3% are schizo. So in fact it is NOT more likely for lefties to be schizo, even though a larger PROPORTION of schizos are lefties. There are still far more depressed lefties than schizophrenic lefties. So any given lefty is still more likely to be depressed than schizophrenic.

    What the author should have concluded was: People who are left-handed are more likely to develop psychotic disorders like schizophrenia compared with people who are right-handed. A completely different claim from the one she did make, which is logically and factually incorrect.

  7. Laura Night

    Derp, are you left-handed? That’s crazy talk.

  8. Joe J.

    JR – I don’t have an alternative explanation other than a prior condition that leads to both left-handedness and schizophrenia. They’re not necessarily related to each other at all. I’m Bipolar and right handed. If most people with Bipolar disorder are also right-handed, that doesn’t mean that the two are necessarily causally linked. Granted, left-handedness and schizophrenia are both rare (though, of course, left-handedness isn’t anywhere near as rare as schizophrenia), but just because there’s a correlation between them doesn’t mean they are causally related. I’d really like to know why people are born left-handed in the first place, since there’s no evidence that there’s a genetic link. Perhaps discovering the answer to that might explain the correlation between left-handedness and schizophrenia.

  9. franbev

    Could it be that from childhood western white society encourages lefties to be something they are not (i.e. to be right handed)? And that this affects their psyche as they somehow feel that they are misfits?

  10. Frank Blankenship

    I get it! Wrong handed people are often wrong headed people, too, but what do you think? Maybe you’ve got the wrong wrong, and wrong is actually correct. I mean I don’t see mental patients as a major force behind rapacious exploitation, global warming, corporate imperialism, or mass extinction of wildlife. Maybe these lefties are actually our best hope for saving life on the planet. Anyway, I’d like to point out that there seems to be a lot wrong with those righties in power as well. Perhaps you’ve noticed it on occasion.

  11. Dex

    Richard Bentall said something like – Schizophrenia is a disease which has no particular symptoms, no predictable course and no effectice treatments- Thus it is always hard to know what anyone means when they say someone is Schizophrenic and we might conclude thus that since left handed people are dominanted by right brain thought processes this might reflect prejudices in the thinking of those doing the diagnoising?
    Or else it reflects a propensity to be victimised by certain kinds of bullying due to a still latent hostility to left handedness!

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