Letter and category fluency in schizophrenic patients: a meta-analysis

Patients with schizophrenia typically demonstrate impairments on semantic and letter fluency tasks but it is possible that these tests demand subtly different cognitive processing: a lexical search based on phonology or orthography or a semantic search based on organization of semantic networks by dimension or attribute. Differences in the performance between these two tasks may imply whether deficits involve difficulties in accessing or traversing connectivities in the semantic system, as opposed to those based on linguistic units. In this meta-analysis, we reviewed 13 studies (N=915) in an attempt to clarify whether schizophrenic patients are in fact differentially impaired in semantic fluency. Results from analyses indicated that schizophrenic patients are disproportionately deficient in category fluency (d=1.23 for semantic and 1.01 for letter fluency with minimal overlap of confidence intervals of weighted d's) suggesting that compromises the semantic system may be present in schizophrenia and perhaps play a role in the symptomatic anomalies exhibited in this patient population.