Premorbid IQ in Schizophrenia: A Meta-Analytic Review
Objective: Over the past three decades, there have been significant changes in the diagnostic criteria for schizophrenia as well as changes in measurement of IQ. The last quantitative review of the literature on premorbid IQ in schizophrenia was published more than two decades ago. Since that time, there have been many published studies of data sets pertaining to this issue. The purpose of the present review was to provide an updated meta-analysis of premorbid IQ in individuals who later develop schizophrenia. Method: The authors performed a systematic literature search, which yielded 18 studies that met criteria for the meta-analysis. Inclusion criteria were 1) premorbid psychometric measures of IQ in subjects who were later diagnosed with schizophrenia, schizoaffective disorder, or schizophreniform disorder, 2) similar comparison data, and 3) sufficient data for calculation of an effect size. The analogue to the analysis of variance method was used to model between-study variance due to key study-design...