基于似然率方法的语音证据评价

法庭话者识别技术引入我国已有二十多年,目前该技术已经广泛应用于各类刑事和民事案件中。纵观世界各国的法庭证据评价体系,除了DNA证据以外,其他证据检验鉴定结论的表述通常有三种:同一认定、否定排除和倾向性意见。简单肯定和否定的结论存在很大的弊端,即过高估计了证据的力度,因而有时可能会造成错案。鉴于此,国外一些学者提出在鉴定结论的表述和价值评判上引入基于贝叶斯理论的"似然率"方法。本文结合目前的法庭话者鉴别方法,重点介绍基于贝叶斯理论下的"似然率"理论体系,并阐明该方法的优越性、局限性以及一些亟待解决的问题。     

证据证明力评价的似然率模型

从概率论的视角看,证据与待证命题是否相关,取决于证据能否改变法官对命题为真的概率评价,证明力的大小则取决于这种改变的程度。似然率模型是一种评价证据证明力的量化方法,它可以统一描述证据“能否”以及在“何种程度”上影响人们对待证命题为真的概率评价。似然率模型有助于法官心证形成过程的明示化、规范化和科学化,对防止法官滥用自由裁量权具有重要的现实意义和应用价值。许多国家普遍应用似然率模型以评价DNA证据的证明力,但有更多问题尚待进一步研究。     

计算混合样本似然率方法的分析与探讨CSCD

目的对混合样本似然率的四种计算方法进行分析和探讨。方法以2013年CNAS-T0757能力验证的1例样本为例,使用四种常用方法(无限制性组合的似然率法、Clayton等的计算方法、p^2定律的计算方法和ISFG推荐方法)分别计算似然率,并进行比较。结果 Clayton等的计算方法、ISFG推荐方法得出的似然率最高,其次为无限制性组合的似然率法得出的结果,p^2定律得出的似然率最低。结论无限制性组合的似然率法最大程度兼顾了信息的保留及鉴定人的保护。     

法庭语音证据评价的范式转变及其进路

法庭科学领域正经历着一场证据评价的范式转变。长期以来,法庭科学不断面临着“科学性”的质疑、挑战和信任危机。为了更好地满足法庭对证据技术的“科学性”要求,提高其准确性、可靠性、客观性和透明性,国际上提出了效仿DNA分型检验,“以实证为基础、基于数据方法进行概率评估,并通过错误率估算表明其局限性”的证据评价新范式。法庭语音证据技术作为法庭科学的分支之一,也同样面临范式转变这一历史选择。首先,从语音证据技术的历史发展出发,分析传统语音证据评价范式的主要特点及其存在的问题。其次,从内在因素和外在因素两个方面分析论证语音证据评价范式转变的发生逻辑。再次,从逻辑框架、技术方法和验证方法三个方面阐述法庭语音证据评价新范式的核心要素和技术流程。最后,结合法庭语音证据评价新范式的国内外发展现状,提出我国语音证据评价新范式的发展路径。     

X-STR分型用于亲缘关系鉴定的似然率计算

目的推导X染色体短串联重复序列(X-short tandem repeat,X-STR)分型用于两个体间亲缘关系鉴定的似然率计算公式。方法根据不同亲缘关系的两个体间的血缘同一系数获得两个体特定的联合基因型概率(X值),计算两无关个体特定的联合基因型概率(Y值),从而求得似然率(X/Y)。结果推导出女性-女性、女性-男性、男性-男性个体间不同亲缘关系各种基因型组合的似然率计算公式,并通过案例验证。结论推导的根据X-STR分型计算两个体间亲缘关系的似然率计算方法简便、准确,为X-STR基因座在疑难亲缘关系鉴定中发挥其更大应用价值奠定了基础。     

X-STR双亲鉴定的似然率和平均排除概率分析

目的推导X-STR亲父疑母女孩和双亲皆疑女孩鉴定的似然率(LR)和平均排除概率(MEC)公式,并以随机模拟法对MEC公式进行实验验证.方法本研究首先根据X-STR亲父疑母女孩(AM)和双亲皆疑女孩(AP)鉴定的LR和MEC定义,分别推导MECAM、LRAM、MECAP和LRAP的数学公式,依据19个X-STR基因座上的...     

基于语音情感分析系统的语音压力测谎

目的探究语音情感分析系统(Layered Voice Analysis,LVA)在不同情况下的表现,并通过分析数据找出影响系统识别率的因素。方法设置两种不同场景对20名研究对象进行提问,并录音。通过LVA语音系统对语音样本进行分析,使用SPSS统计软件对系统生成的参数进行统计分析。结果在未告知研究对象实验真相的情况下LVA语音系统平均识别率为91.75%,要远高于研究对象在知情情况下的识别率。在询问过程中,当未涉及敏感问题时,随着时间的推移研究对象的心理压力逐渐减小。结论LVA语音系统具有良好的情感分析和识别能力,可为司法工作提供参考。     

伪装语音的自动话者识别研究

本文以语音自动话者识别系统为平台,对实际案件中出现频率较高的10种伪装语音类型进行自动话者识别测试。通过对20位发音人的正常语音和10种类型伪装语音的话者辨认和话者确认测试,分析不同语音伪装类型对自动话者识别的影响。该结果对于深入认识伪装语音的特性及其话者识别研究具有重要意义,也为自动话者识别技术的改进提供了参考。     

利用共振峰相对强度特性鉴别双胞胎语音

话者鉴别的一个基本前提是“个体间的语音差异大于个体的语音变异”。本文对30对双胞胎正常朗读语音的共振峰强度特性进行了定量测量、比较、分析,统计得出了共振峰相对强度特性在检验双胞胎语音中的置信度与判阈。     

案件语音证据的收集与查证

公安视听技术是侦查破案一线急需的新技术。事实上,现在许多一线部门已经认识到涉案语音的重要作用。2001年春天某日21时,辽宁省本溪县上堡村发生一起5岁男孩被绑架案,公安人员第二天一早就赶到被害人杜某家安装调试录音电话,果然录制到了绑匪两次催要赎金的电话。警方确认了犯罪嫌疑人并提取了语音样本,中国刑警学院分析后认为,嫌疑人语音样本与两次电话中的一次的语音高度相似,依此线索该案很快告破。黑龙江的一起人身伤害案,本来被告已经承认伤害事     

似然比在法庭说话人确认中的应用

本文把成功应用于DNA检验的证据评估方法（似然比）应用于法庭语音证据评估之中,提取语音的LPC作为识别特征,并使用45人电话对话录音中元音/a/作为样本进行了测试。结果表明该方法不仅能正确识别说话人,而且能根据当前嫌疑人样本和问题语音样本的差异,量化该语音样本作为证据的力度,为法庭提供科学合理的证据评估结果和科学解释。同时,自动特征提取的引入比起人工提取共振峰特征,提高了工作效率,识别系统性能也获得大幅提升。     

Error Rates,Likelihood Ratios,and Jury Evaluation of Forensic Evidence

Forensic examiners regularly testify in criminal cases, informing the jurors whether crime scene evidence likely came from a source. In this study, we examine the impact of providing jurors with testimony further qualified by error rates and likelihood ratios, for expert testimony concerning two forensic disciplines: commonly used fingerprint comparison evidence and a novel technique involving voice comparison. Our method involved surveying mock jurors in Amazon Mechanical Turk (N = 897 laypeople) using written testimony and judicial instructions. Participants were more skeptical of voice analysis and generated fewer “guilty” decisions than for fingerprint analysis (B = 2.00, OR = 7.06, p = <0.000). We found that error rate information most strongly decreased “guilty” votes relative to no qualifying information for participants who heard fingerprint evidence (but not those that heard voice analysis evidence; B = −1.16, OR = 0.32, p = 0.007). We also found that error rates and conclusion types led to a greater decrease on “guilty” votes for fingerprint evidence than voice evidence (B = 1.44, OR = 4.23, p = 0.021). We conclude that these results suggest jurors adjust the weight placed on forensic evidence depending on their prior views about its reliability. Future research should develop testimony and judicial instructions that can better inform jurors of the strengths and limitations of forensic evidence.     

Performance Study of a Score‐based Likelihood Ratio System for Forensic Fingermark Comparison

In this article, the performance of a score‐based likelihood ratio (LR) system for comparisons of fingerprints with fingermarks is studied. The system is based on an automated fingerprint identification system (AFIS) comparison algorithm and focuses on fingerprint comparisons where the fingermarks contain 6–11 minutiae. The hypotheses under consideration are evaluated at the level of the person, not the finger. The LRs are presented with bootstrap intervals indicating the sampling uncertainty involved. Several aspects of the performance are measured: leave‐one‐out cross‐validation is applied, and rates of misleading evidence are studied in two ways. A simulation study is performed to study the coverage of the bootstrap intervals. The results indicate that the evidential strength for same source comparisons that do not meet the Dutch twelve‐point standard may be substantial. The methods used can be generalized to measure the performance of score‐based LR systems in other fields of forensic science.     

Forensic Gait Analysis and Recognition: Standards of Evidence Admissibility

Gait is one biological characteristic which has attracted strong research interest due to its potential use in human identification. Although almost two decades have passed since a forensic gait expert has testified to the identity of a perpetrator in court, the methods remain insufficiently robust, considering the recent paradigm shift witnessed in the forensic science community regarding quality of evidence. In contrast, technological advancements have taken the lead, and research into automated gait recognition has greatly surpassed forensic gait analysis in terms of the size of acquired datasets and demographic variability of participants, tested variables, and statistical evaluation of results. Despite these advantages, gait recognition presents with different problems which are yet to be resolved. Therefore, courts should treat gait evidence with caution, as they should any other form of evidence originating from disciplines without fully established codes of practice, error rates, and demonstrable applications in forensic scenarios.     

Evaluation of a Visualization Assay for Blood on Forensic Evidence

In forensics, bloodstains on dark fabrics might be invisible for the naked eye. Although several visualization, presumptive, and confirmatory blood tests have been developed, all have one or more disadvantages, especially on DNA analysis. We report here the use of a visualization assay that can visually detect blood drops up to 1/20 dilution. In this assay, the fabric is placed between two wet filter papers and covered by glass surfaces on both sides. Pressure is applied on the glass surfaces in which bloodstains transfer onto the filter papers through capillary forces. Detected stains can be tested with other more sensitive presumptive blood tests performed on the filter paper. Even more, DNA analysis can be performed on the transferred bloodstains. The presented visualization assay is easy to perform, extremely cheap, requires little hands on time, and does not affect bloodstain pattern analysis.     

论法庭证据评估体系的发展

随着法律和科学的发展,人们对部分传统的法庭科学产生了质疑。本文探讨了传统法庭证据检验的弊端和目前国际上法庭科学证据的接纳原则,推出了似然比法庭证据检验评估体系,包括似然比对证据强度的量化方法、检验结论的科学解释方法和法庭识别系统可靠性的评估方法。     

言词证据可以作为司法会计鉴定证据

目前在理论界和司法会计鉴定实践中,有关言词证据能否作为司法会计鉴定证据的争议较多.笔者认为,从现实实践的层面来看,还是从法律法规的规定和偿理研究的层面来分析,言词证据都可以并且应当作为司法会计鉴定证据.     

司法会计鉴定中运用言词证据的探讨

言词证据能否作为司法会计鉴定的依据,在司法会计理论界一直存有争议。从司法会计实践中我们发现,涉及财务会计内容的言词证据具有能够反映财务事实的起因、过程和情节的优点,它有助于我们在司法会计鉴定中判断财务会计事实的性质,分清财务会计错误事项形成的过程和原因。只要我们在司法会计鉴定中克服言词证据不稳定等有关问题,科学地运用言词证据,发挥言词证据在司法会计鉴定中的特殊作用,这将有助于我们提高司法会计鉴定质量和司法会计工作的发展。