Data Science LAPD COLLABORATION In the absence of mathematically validated approaches, forensic specialists aim to conduct studies that show how well humans perform certain tasks. A handwriting expert in the LAPD is working on one such study, part of which aims to test the current assumption that the more complex a person’s signature, the better the analysis. As Stern explains it, when it comes to distinguishing between a simulated (forged) and genuine signature, examiners feel that “if someone just does a scribble, it’s a little bit easier to forge and harder to distinguish. So the more bells and whistles a signature has, the stronger the conclusion.” Stern and Bill Thompson, UCI professor emeritus of criminology, law and society, are helping the LAPD expert to plan and carry out the study to determine whether there’s data to back this assumption. To start, handwriting experts analyzed 123 signatures to subjectively assess their complexity using three- and five-point scales. Stern, with help from statistics graduate students Eric Lai and Shuying Zhu, analyzed that data to determine the consistency of the judgments. Now, they are trying to come up with an objective way to measure complexity using certain measures and characteristics derived from the signatures. “Right now, we’re looking at the distribution of angles in the writing strokes that make up the signature,” says Stern. “Are the strokes primarily slanted or vertical, and does that relate to the examiners’
judgments of complexity?” The final step for the LAPD study will then be to estimate performance as a function of complexity. “If this all works out,” says Stern, “then the study will provide data that will allow examiners to say, ‘For a highly complex signature, based on the LAPD study, we get it right X percent of the time.’ ” APPLYING STATISTICAL METHODS Can an examiner match a certain handwriting sample to the writing of a given suspect? Can an examiner match this fingerprint from the crime scene to that of a suspect? Can an examiner tell what caused a particular bloodstain pattern at the crime scene? Questioning signature authenticity is just one of many areas that can leverage statistics — and pattern matching in particular — to find more objective and reliable methods of analysis. In fact, Stern isn’t the only ICS researcher conducting research in this area. Computer Science Professor Charless Fowlkes and Chancellor’s Professor of Computer Science Padhraic Smyth are also involved in CSAFE projects (see the “Additional CSAFE Projects” sidebar on page 5). By bringing statistics and computer science tools to bear on forensic science questions, these ICS researchers are bridging the gap between research and application, furthering their own work while helping to ensure that justice is served — with reliable and valid methods.
Working with LAPD handwriting experts who analyze genuine (left) and simulated (right) signatures, Professor Hal Stern is trying to assess their performance as a function of the signature’s complexity. (The images are from a database of synthetic signatures.)
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2018 YEAR IN REVIEW