Forensic Sci Med Pathol (2011) 7:53–62 57 Fig. 12 Jig saw blade kerf Fig. 14 Hand saw blade kerf Fig. 13 Hand saw blade indicate the P-value is less than 0.01%; thus, the hypothesis that both covariates are negligible is not rejected. Therefore, the maximum likelihood estimates are signiﬁcant. Results Figure 21 shows the boxplots of the kerf widths from the ten saws considered. When the kerf width is approximately 2.6 mm, the probability that the saw is a cut-off saw or a circular saw is approximately 0.50. It suggests that the cut- off saw and circular saw share similar medians; however, the kerf widths for the circular saw are more varied than the cut-off saw. This variation is possibly due to single or Fig. 15 Reciprocating blade multiple factors. Some factors that could account for the differences in range of widths between the two saws are hand, wrist or arm movement while sawing which may affect the lateral movement of the blade, cutting rate, and blade vibration. Also, wear on the bearings could account for differences in the range of widths between kerfs pro- duced by the two saws. The cut-off saw is attached to a steel frame and the saw movement is controlled by a hinge. Figure 1 suggests that there is a linear pattern among the other eight saws. In order to estimate the prediction error of the models, repeated stratiﬁed tenfold cross-validations were conducted. Therefore, regular cross-validation might not be sufﬁcient, while repeated cross-validation provides more evidence about the prediction error of the models. 123