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Intra- and Inter-variability of Footwear Test Impressions: An Inter-active Workshop Christopher Hamburg, Oregon State Police Jeff Jagmin, Washington State Patrol
Course Concepts • Based upon the Northwest Association of Forensic Scientists Special Research Topics • Collaborative based; mentor(s) guiding research but all participants work together to “solve” a problem or answer a question • Data will be gathered with the intent of being formally published
Problem • When comparing physical size of a test impression to a questioned impression, what constitutes a significant difference? • If there is a difference, is that caused by physical differences between the examiner and the wearer at the scene, can it be attributed to “normal” variation, or is it because a different shoe made the impression?
Current State of Affairs • When physical size is different • “…consider scaling, perspective and other issues.” SWGTREAD Guide for the Examination of Footwear and Tire Impression Evidence (03/2006) • What do you do when these issues are not considered to be contributing factors?
Current State, continued • What is “Different”? - A characteristic or feature that is so strong and reliable that it, in itself, demonstrates that the particular known footwear or tire was not the source of and did not make the impression. Usually a difference will be a different class characteristic, such as the specific design or specific physical size of the design. Normal variations in the impression process, the absence of cuts in a questioned impression that appear on the footwear or tire, or the normal advancement of wear with time do not necessarily constitute a comparative difference.(A difference should not be confused with a Dissimilarity.) SWGTREAD, Standard for Terminology Used for Forensic Footwear and Tire Impression Evidence (03/2013)
Current State, continued • Or maybe it’s a “Dissimilarity”: When a characteristic has the appearance of being potentially different but lacks sufficient detail for confirmation.SWGTREAD, Standard for Terminology Used for Forensic Footwear and Tire Impression Evidence (03/2013) So, does “Different” mean “Different”??
Current State, continued There is currently no known contemporary research that addresses the “normal variation in the impression process” as it relates to physical size! There is currently no known published research that addresses the differences in examiners’ physical attributes (foot size, weight, gait, etc.) and how this might affect test impressions!
Basic questions whichwe should be able to answer by the end of the workshop: How much physical size variation is there when an examiner makes multiple test impressions from a single shoe? How much size variation is there when different examiners make test impressions of the same shoe? And while we’re at it: Are different examiners able to repetitively capture randomly acquired characteristics (RACs) in their test impressions?
Our Approach and Stations • Foot measurements • Test Impression creation • Measuring and inputting of data • Statistical analysis
Foot Measurements • Brannock device • Typical shoe size(s)
Data to Record • For Each participant • Foot size (by Brannock Device) • Typical Shoe size (for athletic style shoes) • Height • Weight • Special considerations (pronation, supination, previous injury, etc.)
Test Impression Creation • Shoes • 1 pair of Converse Chuck Taylor All-Star of a size 9, 11 and 13 • 1 pair of Nike Air Max of a size 9, 11, 13, and 15 • Inkless pad and sensitized paper • A total of 21 test impressions for each person • Use a normal walking motion
Assessment, Measuring,and Inputting of Data • Test Impressions evaluated and scanned • Files opened in Photoshop • Measurements • Length • Width • Data entered into Excel
As time permits • Open the class to have other symposium attendees contribute to the data pool by making test impressions with the aid of the workshop participants.
Statistical Analysis • Range, mean, and standard deviation calculated for each participant for each shoe • Range, mean, and standard deviation calculated for each shoe (multiple participants) • Comparison of data vs participants’ physical attributes (eg. Length mean shoe A vs foot size, width mean shoe A vs weight)
Review and Follow up • All Data compiled and shared with participants • Participants and Mentors collaborate to formalize and interpret data for publication