Browsing by Author "Ringrose, Trevor J."

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    Alternative bootstrap confidence regions for multiple correspondence analysis
    (Taylor & Francis, 2024-05-07) Ringrose, Trevor J.
    A new approach for constructing elliptical bootstrap confidence regions for Multiple Correspondence Analysis is proposed, where the difference in method follows directly from the adoption of a different objective criterion to previous approaches. This includes a new correction for the well-known problems caused by the diagonal of the Burt matrix. Simulation experiments show that the method performs reasonably well in many cases, with exceptions being noted. Simulated data sets with known structure are also used to illustrate cases where the proposed method produces results in line with what would be expected, but some alternatives do not.
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    Assessing the quality of footwear marks recovered from simulated graves
    (Elsevier, 2020-07-29) Stephens, Madeleine; Errickson, David; Giles, Stephanie B.; Ringrose, Trevor J.
    Footwear marks are one of the most frequently encountered evidence types recovered from a crime scene and can provide valuable scene intelligence regarding potential suspects. It has been acknowledged that impressions of footwear and tools can be recovered from graves, but previous studies have only focused on tool mark recovery. This has led to a lack of published information regarding footwear mark recovery from graves. It is therefore important to demonstrate whether the recovery of footwear marks is feasible and, if so, under what conditions this can be achieved. To address recovery, this study, placed 60 three dimensional (3D) impressions of footwear marks within 60 simulated graves. This was done to assess time (1, 2, 4 months) and at known depths (20, 30, 40 cm). The footwear marks within the graves were covered with clothing or left uncovered. The shoe’s design patterns were grouped and counted in a photographic comparison between the 3D footwear impressions, placed within the test-pits, and any recovered impressions. A grading system was adapted by the authors to score the quality of footwear impressions observed during recovery. The results demonstrate that the preservation and recovery of footwear impressions from graves is feasible. The simulated graves covered with clothing showed better preservation of footwear impressions, but there was no clear evidence that time or depth had an effect. The authors note that careful consideration and vigilant excavation skills are needed when excavating graves which may bear potential footwear marks, as their recovery will lead to an increased amount of intelligence that can link suspects to homicide scenes.
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    Parametrization of the calcaneus and medial cuneiform to aid potential advancements in flatfoot surgery
    (MDPI, 2024-02-29) Cai, Yanni; Pascoletti, Giulia; Zioupos, Peter; Budair, Basil; Zanetti, Elisabetta M.; Ringrose, Trevor J.; Junaid, Sarah
    Introduction: Flatfoot is a condition commonly seen in children; however, there is general disagreement over its incidence, characterization and correction. Painful flatfoot accompanied with musculoskeletal and soft tissue problems requires surgery to avoid arthritis in adulthood, the most common surgical approach being two osteotomies to the calcaneus and medial cuneiform bones of the foot. Objectives: This study focuses on the parametrization of these two bones to understand their bone morphology differences in a population sample among 23 normal subjects. Population differences could help in understanding whether bone shape may be an important factor in aiding surgical planning and outcomes. Methods: A total of 45 sets of CT scans of these subjects were used to generate surface meshes of the two bones and converted to be iso-topological meshes, simplifying the application of Generalized Procrustes Analysis and Principal Component Analysis, allowing the main sources of variation between the subjects to be quantified. Results: For the calcaneus, 16 Principal Components (PCs) and, for the medial cuneiform, 12 PCs were sufficient to describe 90% of the dataset variability. The quantitative and qualitative analyses confirm that for the calcaneus PC1 describes the Achilles attachment location and PC2 largely describes the anterior part of the bone. For the medial cuneiform, PC1 describes the medial part of the bone, while PC2 mainly describes the superior part. Conclusion: Most importantly, the PCs did not seem to describe the osteotomy sites for both bones, suggesting low population variability at the bone cutting points. Further studies are needed to evaluate how shape variability impacts surgical outcomes. Future implications could include better surgical planning and may pave the way for complex robotic surgeries to become a reality.
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    Simplifying multivariate second-order response surfaces by fitting constrained models using automatic differentiation.
    (Asa American Statistical Association, 2005-08-01T00:00:00Z) Forth, Shaun A.; Ringrose, Trevor J.
    Multivariate regression models for second-order polynomial response surfaces are proposed. The fitted surfaces for each response variable are constrained so that when expressed in their canonical forms they have features in common, such as common stationary points or common sets of eigenvectors. This can greatly reduce the number of parameters required and make the set of surfaces easier to interpret together, at the cost of a greater computational burden. However, the use of automatic differentiation within the package Matlab is shown to be easy and to reduce this burden considerably. We describe the models and how to fit them and derive standard errors, and report a small simulation study and an application to a dataset.
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    A statistical approach to proof testing
    (2008-10-06T00:00:00Z) Horsfall, Ian; Ringrose, Trevor J.; Watson, Celia H.
    Police body armour has undergone rapid evolution, and this is due in part to a relatively simple type approval process which matches relatively small numbers purchased by individual police forces. However, as body armour technology and usage has increased there has been a gradual change of emphasis from solving the immediate protection problems of highly specialised systems towards quality assurance towards of a standard item of equipment. In addition, as the amount and age of armour in service increases, concerns have been raised about methods for ensuring the continued performance over long periods of use or over long production runs. These factors have drawn attention to the statistical significance of existing proof tests, in which armour systems are subjected to small numbers of stabs or ballistic tests. A number of approaches have been suggested including the addition of a V50 ballistic limit test to provide a fully quantitative measure of performance [1]. However this approach also lacks statistical rigour and further enhancements such as regression analysis [2,3] have been suggested to remedy this. In the current work a different statistical approach is suggested in which conventional proof tests can be used to produce statistically robust data of known significance. Initial trials on current police body armour showed that ballistic penetration and knife penetration were similar as the data was highly random and it was difficult to statistically predict individual test results. Ballistic blunt trauma followed a more predictable pattern with simple and easily predicted test-to-test variation allowing good predictions to be made. For the knife and ballistic penetration tests two approaches have been investigated. One method is a point estimate approach that determines failure probability as a simple ratio of pass or fail. Therefore to achieve a failure probability of lower than 0.1 (10%) no more than 1 failure in 10 would be allowed. The second option would be determine how many successful tests were needed to be sure (for instance to 95% probability) that the failure rate was no more than 0.1. This second approach is more severe and it has been shown that at least 28 successful tests are required in order to be reasonably sure that the failure rate is less than 0.1. This paper will demonstrate the development of the statistical model which has been used within 2007 HOSDB body armour standards and shows how it is applied in both type approval and batch testing.