Left-handedness could be associated with a higher risk of developing schizophrenia, according to a new study. Researchers from Yale University have determined that individuals suffering from psychotic disorders, a disproportionate amount of patients are lefties – about four times the global average. The findings support the current hypothesis that different brain hemispheres contribute to different types of mental illness.

The study, which is published in the online journal SAGE Open, sought to investigate the relationship between hand dominance and mental illness. Specifically, the researchers wanted to know whether left-handedness is associated with any particular psychiatric conditions. Although the link has been subject to similar scientific inquiry in the past, few studies have yielded convincing results.

“Prior work has found that patients with schizophrenia are more likely to be left-handed than the general population,” the study authors wrote. “This finding is not consistent, however, and fewer studies have directly compared handedness between psychiatric diagnoses.”

In an attempt to produce a conclusive study, the researcher designed a more rigorous experiment involving 107 individuals from a public psychiatric clinic treating depression, bipolar disorder, schizophrenia, schizoaffective disorder. The team then assessed hand dominance within the group. According to lead author Jadon R. Webb, the findings reveal a remarkably strong link between lefties and conditions characterized by psychosis. "Our results show a strikingly higher prevalence of left-handedness among patients presenting with psychotic disorders such as schizophrenia and schizoaffective disorder, compared to patients presenting for mood symptoms such as depression or bipolar disorder," he said in a press release.

Webb and his colleagues found that while 11 percent of patients diagnosed with mood disorders like depression and bipolar disorder were left-handed, the figure was 40 percent among patients diagnosed with psychotic disorders like schizophrenia and schizoaffective disorder. That is about four times the global average, which currently ranges between 10-12 percent, The New York Times reported. In addition, the researchers noticed that the link was more pronounced for certain ethnicities. "Our own data showed that whites with psychotic illness were more likely to be left-handed than black patients," the authors wrote. "Even after controlling for this, however, a large difference between psychotic and mood disorder patients remained."

According to the National Institutes of Health (NIH), schizophrenia currently affect about one percent of the U.S. population. The debilitating condition, which is characterized by hallucinations and delusions, usually starts to manifest between ages 16 and 30. Although the condition is chronic, symptoms can sometimes be alleviated with antipsychotic medication.

Source: Jadon R. Webb, Mary I. Schroeder, Christopher Chee, Deanna Dial, Rebecca Hana, Hussam Jefee, Jacob Mays, and Patrick Molitor. Left-Handedness Among a Community Sample of Psychiatric Outpatients Suffering From Mood and Psychotic Disorders. SAGE Open, October 2013.