Thermometer and Neurocognitive Tests

  1. Overall, it is important to be able to present the instrument (MATRICS battery) as a different question from the presence or absence of a deficit. That is, if the instruments are inadequate, there might still be a deficit in attention, etc.
  2. The instruments perform adequately and in most of the conventional measurement dimensions: reliability, validity, predictive validity, etc. They reliably predict, for example, the transition to psychosis in the high risk group. In this regard, they are a good index of functioning.
  3. Take, for example, a thermometer. The temperature reading is a relatively good index of the severity of illness (it is not perfect, of course, but it generally has pragmatic value).
  4. Like temperature readings with a thermometer, the neurocognitive tests have the following problems: a) discriminant validity: the battery does not discriminate among the various disorders, b) no evidence of causality: there is nothing of value showing that the presumed deficits cause schizophrenia, c) lack of specificity: the low functioning individuals have showed deficits in practically every domain of functioning; thus, the psychological test do not assess a unique domain nor is there evidence that problems in attention, etc. are more important than other domains, such as insight/flexibility, d) explanatory value: the temperature reading gives some explanation of the body’s reaction to the disease but does not explain the disease itself; similarly, the neurocognitive tests have only a low correlation with negative symptoms and no correlation with positive symptoms and do not explain either.