Research suggests that the ratio of the lengths of the index finger and the ring finger in males may be predictive of a variety of disorders related to disturbed hormonal balance. When the index finger is shorter than the ring finger, this results in a small 2D:4D ratio, pointing to a high exposure to testosterone in the uterus. 
 
 In a new study of 103 male patients diagnosed with schizophrenia and 100 matched healthy male individuals, investigators found that the 2D:4D ratio may be an effective predictor of schizophrenia--there were significant differences between schizophrenia and control groups concerning the ratio of the lengths of the second digit to the fourth digit, as well as its asymmetry, in both hands. 
 
 "Asymmetry index showed moderate discriminatory power and, therefore asymmetry index has a potential utility as a diagnostic test in determining the presence of schizophrenia," said Dr. Taner Oznur, co-author of the Clinical Anatomy study. 
 
 ### ||||| The production of androgens (mostly testosterone) during the early fetal stage is essential for the differentiation of the male brain. Some authors have suggested a relationship between androgen exposure during the prenatal period and schizophrenia. These two separate relationships suggest that digit length ratios are associated with schizophrenia in males. The study was performed in a university hospital between October 2012 and May 2013. One hundred and three male patients diagnosed with schizophrenia according to DSM‐IV using SCID‐I, and 100 matched healthy males, were admitted to the study. Scale for the Assessment of Positive Symptoms (SAPS), Scale for the Assessment of Negative Symptoms (SANS) and Brief Psychiatric Rating Scale (BPRS) were used to assess schizophrenia symptoms. The second digit (2D) and fourth digit (4D) asymmetry index (AI), and the right‐ and left‐hand 2D:4D ratios were calculated. All parametric data in the groups were compared using an independent t‐test. The predictive power of the AI was estimated by receiver operating characteristics analysis. The 2D:4D AI was statistically significantly lower in the patient group than the healthy control comparison group. There were significant differences between the schizophrenia and the control groups in respect of left 2D:4D and right 2D:4D. There was no correlation between AI, left, or right 2D:4D, BPRS, or SAPS in the schizophrenia group. However, there was a negative correlation between left 2nd digit (L2D):4D and the SANS score. Our findings support the view that the 2D:4D AI can be used as a moderate indicator of schizophrenia. Even more simply, the right or left 2D:4D can be used as an indicator. L2D:4D could indicate the severity of negative symptoms. Clin. Anat. 28:551–556, 2015. © 2015 Wiley Periodicals, Inc.
– The length of a man's index and ring fingers have recently been linked from everything to promiscuity and how nice he is to women. The idea is that finger lengths change depending on exposure to testosterone in utero, and it's known as the "2D:4D" ratio. A lower ratio—where the second digit is shorter than the fourth—indicates "greater androgen exposure." In the journal Clinical Anatomy, researchers write that others have previously suggested a link between androgen exposure in the womb and schizophrenia; they take that one step further, hypothesizing the ratio could be predictive of schizophrenia in males. Then they set out to test that hypothesis: In their small study, researchers analyzed the finger lengths of 103 Turkish male patients diagnosed with schizophrenia and 100 healthy male controls. They found "significant differences between schizophrenia and control groups concerning the ratio ... in both hands," the researchers report in a press release. The findings occupy opposite ends of the spectrum: The right-hand 2D:4D ratio was "significantly higher" among the schizophrenia group and the left-hand ratio was "significantly lower"—suggesting the two are opposites, perhaps because testosterone "affects finger ratios differently as it acts in different ways on the left and right hemispheres of the brain," per the study. As for those ratios, the researchers found the size of the ratio in the left hand could indicate the severity of negative symptoms in patients. (A recent study found that schizophrenia isn't actually one disease.)