Does operational diagnosis of schizophrenia significantly impact intellectual deficits in psychotic disorders?
WAIS-R IQ scores cannot separate schizophrenia from other adult psychoses—watch negative symptoms instead.
01Research in Context
What this study did
Researchers gave the WAIS-R IQ test to adults with different psychotic disorders. They wanted to see if IQ scores could tell schizophrenia apart from other psychoses.
Half the group had schizophrenia. The rest had schizoaffective or other psychotic disorders. All took the same IQ test in one sitting.
What they found
Overall IQ scores were the same across groups. You cannot use the full-scale number to spot schizophrenia.
Only the subgroup with many negative symptoms showed a small gap: verbal IQ beat performance IQ by a few points.
How this fits with other research
Bouras et al. (2004) extends these results to people who also have intellectual disability. They found the same IQ overlap, but the dual-diagnosis group had worse negative symptoms and daily living skills.
Herrnstein et al. (1979) saw deep cognitive holes in children with schizophrenia. The new adult data do not clash; kids may show bigger deficits that level out by adulthood.
Shi et al. (2020) looked at response inhibition, not IQ. They showed kids with schizophrenia respond more slowly than kids with ASD, while the current paper shows adult IQ scores do not separate schizophrenia from other psychoses at all.
Why it matters
Skip the WAIS-R if you only need to rule in or out schizophrenia in adults. The score sheet will not help you. Instead, track negative symptoms and daily functioning. If you serve adults with dual diagnosis, borrow the checklist from Bouras et al. (2004) to spot who needs stronger support plans.
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02At a glance
03Original abstract
BACKGROUND: Evidence suggests that, as a group, patients with schizophrenia have intellectual deficits that may precede the manifestation of psychotic symptoms; however, how successfully intelligence tests are able to discriminate schizophrenia from other psychotic disorders has yet to be investigated in detail. METHODS: Using Wechsler Adult Intelligence Scale-Revised (WAIS-R) data for 55 inpatients with schizophrenia and 28 inpatients with non-schizophrenic psychotic disorders (NSPD) (schizophreniform disorder, brief psychotic disorder, delusional disorder, psychotic disorder due to a general medical condition, and psychotic disorders not otherwise specified), intelligence performance was compared between schizophrenia and NSPD and among different subtypes of schizophrenia. RESULTS: There were no significant differences in intelligence quotient (IQ), verbal IQ (VIQ) and performance IQ (PIQ) discrepancy, and subtest scores of WAIS-R between the patients with schizophrenia and those with NSPD. These diagnostic groups were not discriminated well by any WAIS-R variables. Schizophrenia patients with prominent negative symptoms, on the other hand, had a significantly larger IQ discrepancy (VIQ > PIQ) than those without prominent negative symptoms and NSPD patients. Intelligence performance in schizophrenia did not differ with respect to diagnostic subtypes and longitudinal courses. CONCLUSIONS: The current study failed to show diagnostic usefulness of WAIS-R in discriminating schizophrenia and other psychoses. A diagnosis of schizophrenia does not significantly impact intellectual deficits in psychotic disorders.
Journal of intellectual disability research : JIDR, 2007 · doi:10.1111/j.1365-2788.2007.00964.x