Meta-analytic evidence of systematic bias in estimates of neuroleptic malignant syndrome incidence

Abstract Objective The aim of this study was to examine published reports for sources of excessive variance in neuroleptic malignant syndrome (NMS) incidence estimates. Data Sources An unrestricted computerized MEDLINE search was conducted with a comprehensive search logic and supplemented by secondary references and a manual search of an extensive personal library. Study Selection Studies were analyzed if they presented original data and provided at least 2 of the following: number of NMS cases, number of patients at risk, or ratio of cases to patients at risk. Twenty-six of the 28 candidate studies met these minimal criteria. Data Extraction Variables included incidence, year of study publication, mean year of NMS occurrence, patient population at risk, study design, diagnostic criteria, and country of origin. Data Synthesis Standard error, which reflects study size, accounted for 90.8% of the variance ( β = .953, P χ 2 = 71.08, P ≪ .001). No other variable was significantly related to incidence. Conclusions Neuroleptic malignant syndrome incidence estimates to date are non–trivially biased such that larger study size (patients at risk) is strongly related to lower observed incidence. Future studies can minimize the contribution of this and other sources of experimental error by incorporating several very feasible recommendations.