无需校准模型,用两种归一化方法提升文本作者验证的证据力评估
Normalisation-Based Likelihood Ratio Estimation for Forensic Authorship Verification

- 提出平方根修正与罕用词修正两种归一化方法,直接从评分生成似然比
- 在15个语料库中表现接近逻辑回归校准,罕用词修正在45%测试中更优
- 减少数据与时间成本,适合实际法医文本分析场景
作者验证(AV)是判断两段文本是否出自同一作者的任务。在法医情境中,证据强度可通过似然比量化。现有多数AV方法基于评分,需额外校准模型以获得可靠似然比,但校准需大量相关数据,获取与准备耗时。本文提出两种新归一化技术——平方根修正与罕用词修正,可在不依赖校准模型的情况下,直接从LambdaG方法生成似然比(Nini et al. 2026)。这些修正旨在缓解长文本或高度重复文本导致的证据强度高估问题。在15个语料库、100至9,500词长度范围内,使用对数似然比成本(Cllr)评估性能。所提方法表现与逻辑回归校准相当,罕用词修正在约45%测试中表现更优(按语料加权)。且当其表现略逊于逻辑回归时,差距常在5%以内;反观逻辑回归较劣时,差距更大。无需训练校准模型显著降低数据需求、时间和复杂度,提升法医文本比对的可及性与透明度。实证表现与实用优势共同支持其在法医场景中的应用。
原文摘要 · Abstract (English)
Authorship verification (AV) is the task of determining whether two texts were written by the same author. In a forensic context, the strength of AV evidence can be quantified using likelihood ratios. Most AV methods are score-based and deriving well-calibrated likelihood ratios from these scores requires a separate calibration model. This, in turn, requires additional amounts of case-relevant data, which is often time-consuming to obtain and prepare. This study proposes two novel normalisation techniques, the Square Root Correction and the Hapax Correction, for deriving likelihood ratios from the AV method LambdaG without the need of a calibration model (Nini et al. 2026). These corrections are designed to mitigate the overestimation of evidential strength that may result from long or highly repetitive texts. Performance is evaluated against logistic regression calibration across fifteen corpora and a range of text lengths (100-9,500 tokens), using the log-likelihood ratio cost (Cllr). The proposed methods achieve performance comparable to logistic regression calibration, with the Hapax Correction outperforming it in approximately 45% of tests (weighted by corpora). Furthermore, performance was more frequently close (within 5%) when the Hapax Correction was outperformed by logistic regression calibration, compared with the reverse comparison. Eliminating the need to train a calibration model reduces data-requirements, time and complexity, thereby increasing the accessibility and transparency of forensic text comparison. This combination of empirical performance and practical advantages supports the adoption of the proposed methods in forensic settings.
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