NCJ Number
223662
Journal
Journal of Forensic Identification Volume: 58 Issue: 4 Dated: July/August 2008 Pages: 469-484
Date Published
July 2008
Length
16 pages
Annotation
This study examined the accuracy and precision of two methods of computer-assisted ellipse fitting for measuring bloodstains: BackTrack Images and Microsoft Office Excel 2003 AutoShapes.
Abstract
The findings show that both methods of computer-assisted ellipse fitting are robust and reliable bloodstain measurement techniques, particularly bloodstains that have obliquely impacted a planar surface. The testing of "accuracy" pertained to the confidence level in similarity between known and measured values, and the testing of "precision" related to similarity between repeated measures of the same standard. Both BackTrack Images and Microsoft Office Excel 2003 AutoShapes were precise to subdegree levels. Measurement accuracy for both methods improved as the blood droplet alpha angle became increasingly oblique, with the empirical observations supporting the applied mathematical framework. Still, confidence in measurement accuracy should not be overstated. The study also showed the superiority of AutoShapes over manual measurement methods, with ease of application to on-scene physical (stringline) or mathematical (tangent) blood source area of origin determination techniques. Four separate samples of bloodstains (n=39) were provided from four different sources. All bloodstains were produced by dropping liquid blood vertically from pipettes so that causal droplets impacted surfaces variably orientated from the vertical. This report describes the assessments of measurement accuracy and measurement precision. 3 tables, 4 figures and 34 references