This study was undertaken to apply a new method of controlling type I error when performing pairw... more This study was undertaken to apply a new method of controlling type I error when performing pairwise comparisons. The Benjamini and Hochberg false discovery rate (FDR) controlling procedures have proved to be very powerful tools in solving many practical problems but have not yet been applied to pairwise comparisons of refractive index of glass samples. Students t-test and Welch test (unequal variance Student's t-test) were applied to all possible pairwise comparisons. The comparisons were made on the basis of refractive index values of 72 glass fragments from different car windows and 69 different fragments from one windscreen. The type I error was controlled by the use of Benjamini and Hochberg false discovery rate (FDR) controlling procedure. To illustrate the importance of controlling type I error when using pairwise comparisons, results of pairwise comparisons with the FDR controlling procedure were compared to those comparisons made without any controlling procedure. Significantly fewer false negative results (false rejection of H0) were found during the use of FDR procedure in the comparison of refractive indices from the same windscreen than when comparing without controlling type I error. The results of application of FDR method were also compared to the results of other post-hoc tests, such as Tukey HSD test and Bonfferoni test. The FDR method has higher power than Bonferroni method and Tukey HSD method and control errors better than comparing without controlling type I error. The method of choice, for pairwise comparison of glass fragments on the basis of refractive index is Welch test with FDR adjustment. The method gave type I errors at level about 5.3% and type II error at about 3.7%.
Two brands of motor oils (Elf and Castrol) that had been used for various periods of time were ex... more Two brands of motor oils (Elf and Castrol) that had been used for various periods of time were examined. The aim was to differentiate these samples (of varying degree of use) on the basis of their infrared spectra, for criminalistic purposes. The correlation method was used. It was found that the FTIR method is capable of providing sufficiently detailed information if some specific fragments of spectra are examined. Hence, it can be concluded that the investigation procedure proposed is adequate.
Third International Symposium on Information Assurance and Security, 2007
Daniel Ramos and Joaquin Gonzalez-Rodriguez, ATVS - Biometric Recognition Group, Universidad Auto... more Daniel Ramos and Joaquin Gonzalez-Rodriguez, ATVS - Biometric Recognition Group, Universidad Autonoma de Madrid, Spain; daniel.ramos@uam.es ... Institute of Forensic Research, Westerplatte 9, 31-033 Krakow, Poland; gzadora@ies.krakow.pl ... Colin Aitken, School of ...
The aim of the presented study was to elaborate a procedure for detect- ing and identifying organ... more The aim of the presented study was to elaborate a procedure for detect- ing and identifying organic accelerants in samples taken from the site of a fire. In the analysis of fire debris, a key-stage is the preparation of samples, encompassing sepa- rating of analytes from the matrix and concentrating them. In the elaborated proce- dure, head-space analysis with passive
Micro-Raman spectroscopy was applied to forensic identification of pigments in paint chips and pr... more Micro-Raman spectroscopy was applied to forensic identification of pigments in paint chips and provided differentiation between paint samples. Sixty-six blue automotive paint samples, 26 solid and 40 metallic were examined. It was found that the majority of the collected Raman spectra provided information about the pigments present. However, in some cases, fluorescence precluded pigment identification. Using laser excitation at longer wavelengths or pretreatment to effect photobleaching often resulted in reduced fluorescence, particularly for solid color samples, and allowed pigment identification. The examined samples were compared pairwise taking into account number, location, and intensity of absorption bands in their infrared spectra. The estimated discrimination power ranged from 97% for solid paint samples to 99% for metallic paint samples.
This study was undertaken to apply a new method of controlling type I error when performing pairw... more This study was undertaken to apply a new method of controlling type I error when performing pairwise comparisons. The Benjamini and Hochberg false discovery rate (FDR) controlling procedures have proved to be very powerful tools in solving many practical problems but have not yet been applied to pairwise comparisons of refractive index of glass samples. Students t-test and Welch test (unequal variance Student's t-test) were applied to all possible pairwise comparisons. The comparisons were made on the basis of refractive index values of 72 glass fragments from different car windows and 69 different fragments from one windscreen. The type I error was controlled by the use of Benjamini and Hochberg false discovery rate (FDR) controlling procedure. To illustrate the importance of controlling type I error when using pairwise comparisons, results of pairwise comparisons with the FDR controlling procedure were compared to those comparisons made without any controlling procedure. Significantly fewer false negative results (false rejection of H0) were found during the use of FDR procedure in the comparison of refractive indices from the same windscreen than when comparing without controlling type I error. The results of application of FDR method were also compared to the results of other post-hoc tests, such as Tukey HSD test and Bonfferoni test. The FDR method has higher power than Bonferroni method and Tukey HSD method and control errors better than comparing without controlling type I error. The method of choice, for pairwise comparison of glass fragments on the basis of refractive index is Welch test with FDR adjustment. The method gave type I errors at level about 5.3% and type II error at about 3.7%.
Two brands of motor oils (Elf and Castrol) that had been used for various periods of time were ex... more Two brands of motor oils (Elf and Castrol) that had been used for various periods of time were examined. The aim was to differentiate these samples (of varying degree of use) on the basis of their infrared spectra, for criminalistic purposes. The correlation method was used. It was found that the FTIR method is capable of providing sufficiently detailed information if some specific fragments of spectra are examined. Hence, it can be concluded that the investigation procedure proposed is adequate.
Third International Symposium on Information Assurance and Security, 2007
Daniel Ramos and Joaquin Gonzalez-Rodriguez, ATVS - Biometric Recognition Group, Universidad Auto... more Daniel Ramos and Joaquin Gonzalez-Rodriguez, ATVS - Biometric Recognition Group, Universidad Autonoma de Madrid, Spain; daniel.ramos@uam.es ... Institute of Forensic Research, Westerplatte 9, 31-033 Krakow, Poland; gzadora@ies.krakow.pl ... Colin Aitken, School of ...
The aim of the presented study was to elaborate a procedure for detect- ing and identifying organ... more The aim of the presented study was to elaborate a procedure for detect- ing and identifying organic accelerants in samples taken from the site of a fire. In the analysis of fire debris, a key-stage is the preparation of samples, encompassing sepa- rating of analytes from the matrix and concentrating them. In the elaborated proce- dure, head-space analysis with passive
Micro-Raman spectroscopy was applied to forensic identification of pigments in paint chips and pr... more Micro-Raman spectroscopy was applied to forensic identification of pigments in paint chips and provided differentiation between paint samples. Sixty-six blue automotive paint samples, 26 solid and 40 metallic were examined. It was found that the majority of the collected Raman spectra provided information about the pigments present. However, in some cases, fluorescence precluded pigment identification. Using laser excitation at longer wavelengths or pretreatment to effect photobleaching often resulted in reduced fluorescence, particularly for solid color samples, and allowed pigment identification. The examined samples were compared pairwise taking into account number, location, and intensity of absorption bands in their infrared spectra. The estimated discrimination power ranged from 97% for solid paint samples to 99% for metallic paint samples.
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