The Chumbley score for two tool-mark profiles

Compares two striated tool-mark profiles by the deterministic Chumbley score (Chumbley et al. 2010; Hadler and Morris 2018): each profile is trimmed and detrended by its lowess smooth, the pair of windows of wopt points with the largest correlation fixes the shift, and windows of wval points at that shift are compared with windows at other shifts by a standardised Wilcoxon rank-sum statistic.

Usage

chmb(a, b, wopt, wval, coarse = 0.25)

Arguments

a, b

The two profiles: finite numbers (heights along the mark).

wopt, wval

The window lengths of the optimisation and validation steps: whole numbers from 2 with wval <= wopt.

coarse

The lowess span of the detrending: positive.

Value

A named numeric vector: nsame, ndiff (window pairs used), u (the statistic) and p (its upper normal tail; NaN when either set is empty).

References

Chumbley, L. S., Morris, M. D., Kreiser, M. J. et al. (2010). Validation of tool mark comparisons obtained using a quantitative, comparative, statistical algorithm. Journal of Forensic Sciences, 55(4), 953-961. doi:10.1111/j.1556-4029.2010.01424.x

Hadler, J. R. and Morris, M. D. (2018). An improved version of a tool mark comparison algorithm. Journal of Forensic Sciences, 63(3), 849-855. doi:10.1111/1556-4029.13640

Examples

set.seed(1)
m <- cumsum(rnorm(700))
a <- m[1:600] + rnorm(600, sd = 0.2)
b <- m[51:650] + rnorm(600, sd = 0.2)
chmb(a, b, wopt = 120, wval = 30)
#>        nsame        ndiff            u            p 
#> 13.000000000  4.000000000  2.943920289  0.001620417