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Advances toward validating examiner writership opinion based on handwriting kinematics

NCJ Number
Forensic Science International Genetics Volume: 318 Dated: January 2021
Danica M. Ommen; Cami Fuglsby; Michael P. Caligiuri
Date Published
January 2021

This study sought to establish the scientific validity of expert writership opinions and the two-stage approach to evidence interpretation using measures derived from research on handwriting motor control.


A National Research Council report on strengthening forensic science raised concern over the lack of scientific studies that support the validity of examining and interpreting forensic evidence; however, establishing the foundational validity of subjective methods can be challenging. Regression-based procedures were used to address two experimental issues: 1)  the relative contributions of kinematic and pressure features in predicting examiner support for alternate writership propositions when examining pairs of questioned handwriting samples; and 2) the extent to which information about the rarity of the kinematic feature dissimilarity scores improves the accuracy of a predictive model based on dissimilarity alone. Regarding the first question, the study identified a multifactor model consisting of feature dissimilarity scores and their population distributions having correlation coefficients (R2) of 0.84 and 0.88 for the same-writer and different-writers propositions, respectively. Temporal features contributed up to 21 percent to the predictive value of the model, whereas spatial features contributed only 9 percent and pen pressure contributed up to 17 percent. When models were compared reflecting a single-stage process (based on feature dissimilarities) of forming opinions with models reflecting a two-stage process (based on feature dissimilarities and rarity) the study found that the two-stage models had an average of 15.25 percent greater predictive value than single-stage models. These findings support the scientific validity of FDE writership determinations and underscore the importance of the two-stage approach for evidence interpretation. (publisher abstract modified)