Metrological framework for selecting morphological characters to identify species and estimate developmental maturity of forensically significant insect specimens

Accurate age estimates of immature necrophagous insects associated with a human or animal body can provide evidence of how long the body has been dead. These estimates are based on species-specific details of the insects’ aging processes, and therefore require accurate species identification and developmental stage estimation. Many professionals who produce or use identified organisms as forensic evidence have little training in taxonomy or metrology, and appreciate the availability of formalized principles and standards for biological identification. Taxonomic identifications are usually most readily and economically made using categorical and qualitative morphological characters, but it may be necessary to use less convenient and potentially more ambiguous characters that are continuous and quantitative if two candidate species are closely related, or if identifying developmental stages within a species. Characters should be selected by criteria such as taxonomic specificity and metrological repeatability and relative error. We propose such a hierarchical framework, critique various measurements of immature insects, and suggest some standard approaches to determine the reliability of organismal identifications and measurements in estimating postmortem intervals. Relevant criteria for good characters include high repeatability (including low scope for ambiguity or parallax effects), pronounced discreteness, and small relative error in measurements. These same principles apply to individuation of unique objects in general.

Key points

• Metrological rigour can increase in forensic entomology by selecting measurements based on their metrological qualities.
• Selection of high-quality features for morphological identification of organisms should consider these criteria: (1) pronounced discreteness of features (minimising group overlap or maximizing interval); (2) high repeatability of assessment (such as symmetrical width rather than asymmetrical length); (3) small relative error in measurement (selecting the physically largest continuous rigid feature for measurement).
• These metrological principles also apply to individuation of unique objects in general.

     

The Accuracy and Repeatability of Reconstructing Single Bullet Impacts Using the 2D Ellipse Method

When a bullet punctures a surface, it leaves behind a bullet impact, which can be analyzed in order to determine the origin and trajectory path from which a bullet was discharged using many different scientific methods to reconstruct a shooting scene. The purpose of the research was to test the accuracy and repeatability of reconstructing the impact angle of single bullet impacts using the ellipse method. The research was conducted by firing various calibers of ammunition into drywall panels positioned at varying angles of incidence from 88° until ricochet occurred. This was done in order to determine which caliber type and angle of incidence are most accurate and precise for reconstructing a shooting scene. The study examined four caliber types fired into drywall panels, with 5 repeated shots for each of the 11 angles of incidence (n = 220). Furthermore, 31 participants partook in the study to estimate a bullet impact angle of incidence utilizing the ellipse method. The results show that the best performance (accuracy and repeatability) is seen with the measurements of the 0.45 caliber ammunition. When angle of incidences is low (<64°), the performance (accuracy and repeatability) was seen to be better in all caliber ammunitions. Overall, the data provided for single bullet impacts deposited in drywall show that the ellipse method is useful in providing measurements for most crime scene reconstruction purposes and has also demonstrated that results vary depending on the type of ammunition, firearm, and angle of incidence being examined.     

PuriTyper~(TM)法医学纯化试剂盒的性能验证

目的验证PuriTyperTM纯化试剂盒各项性能指标和法医学应用价值。方法收集及制备抗凝血液、常见案件检材(唾液、烟头、精液、毛发、指甲、骨骼及组织块)、斑痕样本(血斑、唾液斑、精斑)以及模拟添加抑制剂和模仿自然环境中放置的血斑。采用PuriTyperTM纯化试剂盒提取纯化并进行DNA定量,IdentifilerTM复合扩增试剂盒扩增,产物经ABI 3130遗传分析仪进行检测,Genemapper软件分析结果,对该试剂盒灵敏度、稳定性、重复性、检材适应性进行测试。结果采用该试剂盒提取0.1～40μL血液分别获得0.042～26.45ng/μL的DNA。3种斑痕样本DNA产量平行试验结果稳定。不同类型检材重复检验所获IPC的CT平均值在27.60至28.03之间。常见案件检材所得分型与已知结果均一致。结论 PuriTyperTM纯化试剂盒能够满足法医DNA检验的要求,对法医学实践具有重要的应用价值。     

Repeatability and reproducibility of comparison decisions by firearms examiners

In a comprehensive study to assess various aspects of the performance of qualified forensic firearms examiners, volunteer examiners compared both bullets and cartridge cases fired from three different types of firearms. They rendered opinions on each comparison according to the Association of Firearm & Tool Mark Examiners (AFTE) Range of Conclusions, as Identification, Inconclusive (A, B, or C), Elimination, or Unsuitable. In this part of the study, comparison sets used previously to characterize the overall accuracy of examiners were blindly resubmitted to examiners to assess the repeatability (105 examiners; 5700 comparisons of bullets and cartridge cases) and reproducibility (191 examiners of bullets, 193 of cartridge cases; 5790 comparisons) of firearms examinations. Data gathered using the prevailing AFTE Range were also recategorized into two hypothetical scoring systems. Consistently positive differences between observed agreement and expected agreement indicate that the repeatability and reproducibility of examiners exceed chance agreement. When averaged over bullets and cartridge cases, the repeatability of comparison decisions (involving all five levels of the AFTE Range) was 78.3% for known matches and 64.5% for known nonmatches. Similarly averaged reproducibility was 67.3%% for known matches and 36.5% for known nonmatches. For both repeatability and reproducibility, many of the observed disagreements were between a definitive and inconclusive category. Examiner decisions are reliable and trustworthy in the sense that identifications are unlikely when examiners are comparing non-matching items, and eliminations are unlikely when they are comparing matching items.     

对习惯权利的当代思考

随着全国大部分城市放开对烟花爆竹的禁令,引发了学界对习惯权利的重新关注。习惯权利的研究重新提上日程。笔者从群体性、自发性、重复性、合理性四个方面对习惯权利的新内涵进行了分析,并以此建构习惯权利的保障机制。     

Testing repeatability and error of coordinate landmark data acquired from crania

This study evaluates issues of precision, repeatability, and validation in three-dimensional (3D) landmark coordinates. Two observers collected 19 homologous cranial landmarks from three skulls during three separate digitizing sessions. Statistical analysis was conducted on the 171 interlandmark distances (ILDs) derived from the original coordinate data. A mixed model ANOVA detected significant within-subject error in 54 of the 171 ILDs (i.e., 32%). A GLM procedure revealed significant between-observer variation in 14 ILDs and significant observer-by-session differences in 13 ILDs. The majority of these differences involved ILDs with type 3 landmarks as endpoints, such as euryon and alare. Unlike type 1 and 2 landmarks which are biologically informative in all directions, type 3 landmarks contain a substantial arbitrary component. Thus, it is not surprising type 3 landmarks displayed significant digitizing error. Given these results, we caution researchers to be mindful of type 3 landmarks measurement discrepancies when selecting landmarks for coordinate data evaluation.     

Exploring the Impacts of Ordinary Laboratory Alterations During Forensic DNA Processing on Peak Height Variation,Thresholds, and Probability of Dropout,

Impacts of validation design on DNA signal were explored, and the level of variation introduced by injection, capillary changes, amplification, and kit lot was surveyed by examining a set of replicate samples ranging in mass from 0.25 to 0.008 ng. The variations in peak height, heterozygous balance, dropout probabilities, and baseline noise were compared using common statistical techniques. Data indicate that amplification is the source of the majority of the variation observed in the peak heights, followed by capillary lots. The use of different amplification kit lots did not introduce variability into the peak heights, heterozygous balance, dropout, or baseline. Thus, if data from case samples run over a significant time period are not available during validation, the validation must be designed to, at a minimum, include the amplification of multiple samples of varying quantity, with known genotype, amplified and run over an extended period of time using multiple pipettes and capillaries.