Exploratory rasch analysis of a static-99R clinical cohort assessment

• Published in: PloS one 2024-07, Vol.19 (7), p.e0307216
• Main Authors: Baudin, Christian, Grimby-Ekman, Anna, Nilsson, Thomas, Wallinius, Märta, Andiné, Peter
• Format: Article
• Language: English
• Subjects: Adult; Annan medicin och hälsovetenskap; Biology and Life Sciences; Classical test theory; Cohort Studies; Computer and Information Sciences; Convictions; Crime prevention; Discriminant analysis; Engineering and Technology; Female; Forensic medicine; Forensic psychiatry; Forensic Science; Humans; Internal validity; Male; Medical and Health Sciences; Medical research; Medicin och hälsovetenskap; Medicine and Health Sciences; Medicine, Experimental; Mental disorders; Mental Disorders - diagnosis; Mental Disorders - psychology; Mental illness; Mentally ill; Middle Aged; Missing data; Other Medical Sciences; People and places; Probability; Probability Theory and Statistics; Psychiatry; Psychometrics - methods; Psykiatri; Quantitative psychology; Rasch model; Recidivism; Recidivism - statistics & numerical data; Regression analysis; Reproducibility of Results; Revisions; Risk assessment; Risk Assessment - methods; Rättsmedicin; Sannolikhetsteori och statistik; Sex crimes; Sex Offenses - psychology; Sexual assault; Social Sciences; Surveys and Questionnaires; Validation studies
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0307216

Modern test theory supplements the more prevalent classic methods for assessing test properties. However, such an assessment of the commonly used sexual recidivism risk assessment instrument, Static-99R, has yet to be attempted. This study evaluated the psychometric properties of said instrument using Rasch analysis. The clinical cohort assessed consisted of individuals with mental disorders convicted of a sexual offense (N = 146). Results showed that the original ten-item Static‑99R did not meet the Rasch model requirements, and revisions of the instrument with seven and nine items each only marginally improved performance. More reliable results could likely have been obtained with a larger, non-clinical sample and a more randomized distribution of missing data. Despite the consistently poor performance of item 3 ("Index non-sexual violence") in all three analyses, reliability was slightly improved by dichotomizing the only two polytomous items in the Static-99R; items 1 ("Age at release from index offense") and 5 ("Prior sexual offenses"). These results may be of interest considering the significant change of splitting the formerly dichotomous item 1 into four different response categories in the revision of Static-99 to Static-99R.