Validity of Simpson-Angus Scale (SAS) in a naturalistic schizophrenia population.
BACKGROUND
Simpson-Angus Scale (SAS) is an established instrument for neuroleptic-induced parkinsonism (NIP), but its statistical properties have been studied insufficiently. Some shortcomings concerning its content have been suggested as well. According to a recent report, the widely used SAS mean score cut-off value 0.3 of for NIP detection may be too low. Our aim was to evaluate SAS against DSM-IV diagnostic criteria for NIP and objective motor assessment (actometry).


METHODS
Ninety-nine chronic institutionalised schizophrenia patients were evaluated during the same interview by standardised actometric recording and SAS. The diagnosis of NIP was based on DSM-IV criteria. Internal consistency measured by Cronbach's alpha, convergence to actometry and the capacity for NIP case detection were assessed.


RESULTS
Cronbach's alpha for the scale was 0.79. SAS discriminated between DSM-IV NIP and non-NIP patients. The actometric findings did not correlate with SAS. ROC-analysis yielded a good case detection power for SAS mean score. The optimal threshold value of SAS mean score was between 0.65 and 0.95, i.e. clearly higher than previously suggested threshold value.


CONCLUSIONS
We conclude that SAS seems a reliable and valid instrument. The previously commonly used cut-off mean score of 0.3 has been too low resulting in low specificity, and we suggest a new cut-off value of 0.65, whereby specificity could be doubled without loosing sensitivity.
Janno
Sven
S
Department of Psychiatry, University of Tartu, Raja 31, 50417, Tartu, Estonia. svenjanno@hot.ee
Holi
Matti M
MM
Tuisku
Katinka
K
Wahlbeck
Kristian
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D014150:Antipsychotic Agents / Q000009:adverse effects; D002908:Chronic Disease; D005260:Female; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000295:instrumentation / Q000592:standards; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000592:standards*; D020734:Parkinsonian Disorders / Q000139:chemically induced* / Q000145:classification*; D012372:ROC Curve; D012559:Schizophrenia / Q000188:drug therapy*; D012680:Sensitivity and Specificity
D014150:Antipsychotic Agents