A sub-analysis by fixation method of the parvalbumin cell density studies in the pre-frontal cortex showed that those studies using paraformaldehyde, a more reliable fixation method, showed a non-significant reduction in patients with schizophrenia compared with healthy controls (Hedges’ g − 0.30; p = 0.05; CI: − 0.59–0.02) as did the formalin/paraffin-prepared studies (Hedges’ g − 0.19; p = 0.35; CI: − 0.60–0.22) (see Fig. 4). The gene discussed is PVALB; the disease is schizophrenia.