An Examination of How Various Statistical Weighting Methods Impact Predictive Validity of the Service Planning Instrument for Women (SPIn-W)

Risk assessments are vital within the criminal justice system, yet research regarding the optimization of these instruments for women is limited. Currently, minimal research is available on the impact various statistical weighting methodologies may have on the prediction of recidivism for women. Using two-year fixed follow-up data from 656 justice-involved women from Maine United States, the current study explored the predictive validity of the Service Planning Instrument for Women (SPIn-W; Orbis Partners, 2007) at the item level and the predictive accuracy of four weighting methodologies. Results from the present study showed that 19 of the 98 items of the SPIn-W were significantly predictive of recidivism. Further, the gender-responsive Nuffield 2.0 weighting method most often evidenced the greatest levels of predictive accuracy across aggregate and domain level scores. Pending replication and cross-validation, the current study suggests that the SPIn-W be updated with the gender-responsive Nuffield 2.0 method to optimize predictive validity.