Journal ol Consulting and Clinical 1'sycltology 1976, Vol. 44, No. 5, 878
A Bias in the Diagnosis of Schizophrenia William Kent Rcade and Michael Wertheimer University of Colorado Research has demonstrated significantly high concordance between twins or other family members when one of them has been found to be schizophrenic. The question arises: If a person has a sibling who was diagnosed as schizophrenic, docs this alone increase the probability that that person will be similarly diagnosed when a diagnostician is aware of this fact? If so, what are the implications for research and clinical practice? A fictitious case history containing behavioral clues that could be interpreted as moderately consistent with a diagnosis of schizophrenia (e.g., introversion, untidiness) but that would not be conclusive (e.g., delusions, hallucinations) was prepared in two forms. The forms were identical except for one sentence, which in the "control" form read, "Mr. S has an identical twin, who 7 years ago joined the army and has visited home only once for a 2-week long slay"; in the "experimental" version it read, "Mr. S has an identical twin, who 4 years ago was placed in a mental hospital with a diagnosis of simple schizophrenia." Respondents were asked to indicate their judgment of the probability that Mr. S was schizophrenic by circling the appropriate number on a scale from 0 to 100 in steps of S; respondents were also asked the number of years of experience they had had in making clinical diagnoses. Fifteen clinical faculty and two interns in child and adult psychology at the University of Colorado Medical Center (M years of experience =; 5.5) served as subjects, with eight in the experimental group and nine in the control group. Requests for reprints and for an extended report of this study should be sent to Michael Wertheimer, Department of Psychology, University of Colorado, Boulder, Colorado 80302.
The mean of the probabilities circled was 39 for the controls and 66 for the experimentals (Mdn = 40 and 68, respectively; p < .01 by MannWhitney U test). There was no difference in the amount of experience of the two groups nor any relationship between years of experience and the probability circled. The information that Mr. S had a twin who was diagnosed schizophrenic almost doubled the raters' estimates of the probability that Mr. S was schizophrenic. Although not surprising, these results do suggest that care must be taken in interpreting studies in which the diagnostician of the sibling had knowledge of the proband, and therefore, perhaps, produced spuriously high concordance rates. Diagnosis of psychopathology should ideally be based on an analysis of individuals' particular symptomatology, that is, their own behavior. Although knowledge that a predisposition to schizophrenia may be inherited can enhance our understanding of the etiology of the syndrome, such knowledge does not directly imply anything about a person's behavior and is, strictly speaking, irrelevant to individual diagnosis. A genetic predisposition is not schizophrenia until it is expressed phenotypically. The magnitude of the demonstrated bias requires caution on the part of the clinician, especially when there arc not enough behavioral clues alone for individual diagnosis. An inappropriate diagnosis might very well result in a psychosocial phenomenon yielding behavior that would ultimately confirm that diagnosis. Therefore, it is suggested that, prior to availing themselves of family history, diagnosticians attempt to obtain relatively conclusive behavioral information, lest they inadvertently increase the likelihood of a diagnosis of psychopathology where none exists.
878
(Received December 30, 1975)
A Bias in the Diagnosis of Schizophrenia William Kent Rcade and Michael Wertheimer University of Colorado Research has demonstrated significantly high concordance between twins or other family members when one of them has been found to be schizophrenic. The question arises: If a person has a sibling who was diagnosed as schizophrenic, docs this alone increase the probability that that person will be similarly diagnosed when a diagnostician is aware of this fact? If so, what are the implications for research and clinical practice? A fictitious case history containing behavioral clues that could be interpreted as moderately consistent with a diagnosis of schizophrenia (e.g., introversion, untidiness) but that would not be conclusive (e.g., delusions, hallucinations) was prepared in two forms. The forms were identical except for one sentence, which in the "control" form read, "Mr. S has an identical twin, who 7 years ago joined the army and has visited home only once for a 2-week long slay"; in the "experimental" version it read, "Mr. S has an identical twin, who 4 years ago was placed in a mental hospital with a diagnosis of simple schizophrenia." Respondents were asked to indicate their judgment of the probability that Mr. S was schizophrenic by circling the appropriate number on a scale from 0 to 100 in steps of S; respondents were also asked the number of years of experience they had had in making clinical diagnoses. Fifteen clinical faculty and two interns in child and adult psychology at the University of Colorado Medical Center (M years of experience =; 5.5) served as subjects, with eight in the experimental group and nine in the control group. Requests for reprints and for an extended report of this study should be sent to Michael Wertheimer, Department of Psychology, University of Colorado, Boulder, Colorado 80302.
The mean of the probabilities circled was 39 for the controls and 66 for the experimentals (Mdn = 40 and 68, respectively; p < .01 by MannWhitney U test). There was no difference in the amount of experience of the two groups nor any relationship between years of experience and the probability circled. The information that Mr. S had a twin who was diagnosed schizophrenic almost doubled the raters' estimates of the probability that Mr. S was schizophrenic. Although not surprising, these results do suggest that care must be taken in interpreting studies in which the diagnostician of the sibling had knowledge of the proband, and therefore, perhaps, produced spuriously high concordance rates. Diagnosis of psychopathology should ideally be based on an analysis of individuals' particular symptomatology, that is, their own behavior. Although knowledge that a predisposition to schizophrenia may be inherited can enhance our understanding of the etiology of the syndrome, such knowledge does not directly imply anything about a person's behavior and is, strictly speaking, irrelevant to individual diagnosis. A genetic predisposition is not schizophrenia until it is expressed phenotypically. The magnitude of the demonstrated bias requires caution on the part of the clinician, especially when there arc not enough behavioral clues alone for individual diagnosis. An inappropriate diagnosis might very well result in a psychosocial phenomenon yielding behavior that would ultimately confirm that diagnosis. Therefore, it is suggested that, prior to availing themselves of family history, diagnosticians attempt to obtain relatively conclusive behavioral information, lest they inadvertently increase the likelihood of a diagnosis of psychopathology where none exists.
878
(Received December 30, 1975)
