Previously, Australian and New Zealand jurisdictions were operating with widely different conclusion scales and terminology in shoe and tire mark comparisons. This study compared the variability in responses to such comparisons through two collaborative trials of six comparison exercises. The first used the status quo in each jurisdiction; the second required respondents to use the conclusion scale recommended by the shoe and tire Scientific Working Group (SWGTREAD) in the United States.
The adoption of the new conclusion scale greatly improved the clarity and comparability of conclusions. Excepting outliers that would likely be negated through technical reviews in casework, the range of conclusions for each comparison was slightly reduced in the second trial. Participants were observed to be conservative in their responses, erring on the side of exclusion rather than inclusion.
A significant observation is that close non-matches may not be detected, even by experienced examiners. It is essential that in conclusions of this type, the examiner makes clear to the court that another shoe of the same pattern and dimensions could have made the mark.
The benefits of a standard conclusion scale and terminology were made clear by this exercise, and therefore the new conclusion scale is recommended for use in Australia and New Zealand.