title: Comparisons of methamphetamine psychotic and schizophrenic symptoms: a differential item functioning analysis.
abstract: The concept of negative symptoms in methamphetamine (MA) psychosis (e.g., poverty of speech, flatten affect, and loss of drive) is still uncertain. This study aimed to use differential item functioning (DIF) statistical techniques to differentiate the severity of psychotic symptoms between MA psychotic and schizophrenic patients. Data of MA psychotic and schizophrenic patients were those of the participants in the WHO Multi-Site Project on Methamphetamine-Induced Psychosis (or WHO-MAIP study) and the Risperidone Long-Acting Injection in Thai Schizophrenic Patients (or RLAI-Thai study), respectively. To confirm the unidimensionality of psychotic syndromes, we applied the exploratory and confirmatory factor analyses (EFA and CFA) on the eight items of Manchester scale. We conducted the DIF analysis of psychotic symptoms observed in both groups by using nonparametric kernel-smoothing techniques of item response theory. A DIF composite index of 0.30 or greater indicated the difference of symptom severity. The analyses included the data of 168 MA psychotic participants and the baseline data of 169 schizophrenic patients. For both data sets, the EFA and CFA suggested a three-factor model of the psychotic symptoms, including negative syndrome (poverty of speech, psychomotor retardation and flatten/incongruous affect), positive syndrome (delusions, hallucinations and incoherent speech) and anxiety/depression syndrome (anxiety and depression). The DIF composite indexes comparing the severity differences of all eight psychotic symptoms were lower than 0.3. The results suggest that, at the same level of syndrome severity (i.e., negative, positive, and anxiety/depression syndromes), the severity of psychotic symptoms, including the negative ones, observed in MA psychotic and schizophrenic patients are almost the same.
authors.affiliation: Department of Psychiatry, Chiang Mai University, Chiang Mai, Thailand. msrisu@yahoo.com
authors.forename: Manit
authors.initials: M
authors.lastname: Srisurapanont
authors.forename: Suwanna
authors.initials: S
authors.lastname: Arunpongpaisal
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Wada
authors.forename: John
authors.initials: J
authors.lastname: Marsden
authors.forename: Robert
authors.initials: R
authors.lastname: Ali
authors.forename: Ronnachai
authors.initials: R
authors.lastname: Kongsakon
mesh_terms: D000328:Adult; D000339:Affect; D019969:Amphetamine-Related Disorders / Q000523:psychology*; D001007:Anxiety / Q000139:chemically induced / Q000523:psychology; D000697:Central Nervous System Stimulants; D003627:Data Interpretation, Statistical; D003866:Depressive Disorder / Q000139:chemically induced / Q000523:psychology; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D008297:Male; D008694:Methamphetamine; D009042:Motivation; D010045:Outpatients; D011569:Psychiatric Status Rating Scales; D011605:Psychoses, Substance-Induced / Q000523:psychology*; D012565:Schizophrenic Psychology; D013060:Speech
chemical_list: D000697:Central Nervous System Stimulants; D008694:Methamphetamine