NCJ Number
187377
Journal
Canadian Society of Forensic Science Volume: 33 Issue: 4 Dated: December 2000 Pages: 173-185
Editor(s)
B. Yamashita
Date Published
December 2000
Length
13 pages
Annotation
Variations in the refractive index (RI) of control glass samples from crime scenes in Canada were investigated.
Abstract
RI data were compiled for four types of flat glass--toughened float glass, non-toughened float glass, non-float glass, and wired glass. Additional control glass samples for each type of glass were simulated from the case data. This was done by standardizing and pooling the data for each type of glass and then drawing a predetermined number of measurements from a given data pool. Mean, standard deviation, and 95 percent and 99 percent confidence intervals were calculated from the larger sets of simulated numerical data. Statistical results for each type of glass were tabulated to assist the forensic scientist in determining how many measurements to make on a control glass before comparison with recovered glass fragments. Based on data for the control glass samples in the current study, it seemed reasonable to conclude that the 95 percent confidence interval of the control should not exceed plus or minus 0.00005 RI units, 90 percent of the time. Thus, about 20 RI measurements would be required when sampling a toughened float glass control and about 10 RI measurements would be required for a non-toughened float glass control. Other types of control glass, namely non-float glass and wired glass, would require a similar number of RI measurements as a sample of non-toughened float glass. Additional statistical results for the control glass samples are appended. 12 references, 6 tables, and 5 figures