This research examined the foundational validity of forensic document examiner (FDE) writership determinations by examining the relationships between FDE strength of support concerning writership propositions and the differences in the kinematic feature dynamic distributions of the two writing samples.
The research team used univariate and multivariate regression procedures to estimate the degree to which kinematic feature dissimilarities account for variability in FDE strength of support for alternate propositions. A finding that FDE writership opinions are statistically associated with these kinematic feature dissimilarity scores would support the scientific basis for handwriting examination and strengthen the validity of the FDE decisionmaking process. The project involved two groups of subjects. Thirty-five writers recruited from the San Diego Sheriff’s Crime Laboratory were instructed to write six phrases from the London Letter and to repeat each phase five times, using both print and cursive writing styles. The second group of subjects consisted of 41 FDEs recruited from North America, Europe, and Australia/New Zealand to participate in a survey of these handwriting samples to obtain strength of support for alternate propositions regarding writership. For handwriting samples written by a single writer, the analysis found that FDEs offered significantly stronger support for a common-source proposition than the alternate proposition that the samples came from different writers. Conversely, for handwriting samples written by different writers, the study found that FDEs offered significantly stronger support for a different source proposition than the alternate proposition that the samples came from the same writer. These findings support the validity of the survey instrument as a tool for obtaining writership opinions under two alternate propositions. Overall, the study provides empirical evidence that supports the validity of expert opinions for admissibility in courts of law under Daubert. Tables and figures are provided.