Kinematic Validation of FDE Determinations about Writership in Handwriting Examination: A Preliminary Study

As with many of the forensic disciplines that rely on feature-comparison methods, there is no “gold standard” against which to test accuracy of handwriting examination. This study examined differences in kinematic features between pairs of handwriting exemplars judged to be from the same writer and compared them with differences in kinematic features for pairs of handwriting exemplars judged to be from different writers. We hypothesized that differences in kinematic features between pairs of handwriting exemplars judged to be from the same writer would be nonsignificant; whereas differences in kinematic features for pairs of handwriting exemplars judged to be from different writers would be statistically significant. Cursive, script and block print handwriting samples were obtained from 37 writers who were asked to write a single word ten times each. High resolution (600 ppi) scanned copies of the original ink and paper samples were submitted to four experienced forensic document examiners (FDEs) for writership determinations. Each score sheet included 5 known (K) handwritten samples and two questioned samples (Q1 and Q2). FDEs were asked to rate the evidence in support for the proposition that the Q samples were written by the K writer using a 4-point scale (ranging from limited or weak support to very strong support for the proposition). Kinematic difference scores derived from dynamic analysis of the handwritten strokes were converted to absolute standardized z-scores with larger z-score reflecting greater differences between K and Q for a given kinematic feature. Findings revealed that several kinematic handwriting features were significantly associated with accurate FDE opinions of acceptance and rejection of the proposition. Significant features included pen pressure, stroke velocity, and straightness variability. Correlational analyses revealed strong associations between specific dynamically recorded stroke features and FDE judgments of writership; particularly for pen pressure and straightness. Results support the use of an independent quantitative measure of feature comparison as a tool for evaluating the foundational validity of subjective feature comparison methods experts use when reaching conclusions about writership.