gbanyan
9d19ca5a31
Major fixes per codex (gpt-5.4) review: ## Structural fixes - Fixed three-method convergence overclaim: added Script 20 to run KDE antimode, BD/McCrary, and Beta mixture EM on accountant-level means. Accountant-level 1D convergence: KDE antimode=0.973, Beta-2=0.979, LogGMM-2=0.976 (within ~0.006). BD/McCrary finds no transition at accountant level (consistent with smooth clustering, not sharp discontinuity). - Disambiguated Method 1: KDE crossover (between two labeled distributions, used at signature all-pairs level) vs KDE antimode (single-distribution local minimum, used at accountant level). - Addressed Firm A circular validation: Script 21 adds CPA-level 70/30 held-out fold. Calibration thresholds derived from 70% only; heldout rates reported with Wilson 95% CIs (e.g. cos>0.95 heldout=93.61% [93.21%-93.98%]). - Fixed 139+32 vs 180: the split is 139/32 of 171 Firm A CPAs with >=10 signatures (9 CPAs excluded for insufficient sample). Reconciled across intro, results, discussion, conclusion. - Added document-level classification aggregation rule (worst-case signature label determines document label). ## Pixel-identity validation strengthened - Script 21: built ~50,000-pair inter-CPA random negative anchor (replaces the original n=35 same-CPA low-similarity negative which had untenable Wilson CIs). - Added Wilson 95% CI for every FAR in Table X. - Proper EER interpolation (FAR=FRR point) in Table X. - Softened "conservative recall" claim to "non-generalizable subset" language per codex feedback (byte-identical positives are a subset, not a representative positive class). - Added inter-CPA stats: mean=0.762, P95=0.884, P99=0.913. ## Terminology & sentence-level fixes - "statistically independent methods" -> "methodologically distinct methods" throughout (three diagnostics on the same sample are not independent). - "formal bimodality check" -> "unimodality test" (dip test tests H0 of unimodality; rejection is consistent with but not a direct test of bimodality). - "Firm A near-universally non-hand-signed" -> already corrected to "replication-dominated" in prior commit; this commit strengthens that framing with explicit held-out validation. - "discrete-behavior regimes" -> "clustered accountant-level heterogeneity" (BD/McCrary non-transition at accountant level rules out sharp discrete boundaries; the defensible claim is clustered-but-smooth). - Softened White 1982 quasi-MLE claim (no longer framed as a guarantee). - Fixed VLM 1.2% FP overclaim (now acknowledges the 1.2% could be VLM FP or YOLO FN). - Unified "310 byte-identical signatures" language across Abstract, Results, Discussion (previously alternated between pairs/signatures). - Defined min_dhash_independent explicitly in Section III-G. - Fixed table numbering (Table XI heldout added, classification moved to XII, ablation to XIII). - Explained 84,386 vs 85,042 gap (656 docs have only one signature, no pairwise stat). - Made Table IX explicitly a "consistency check" not "validation"; paired it with Table XI held-out rates as the genuine external check. - Defined 0.941 threshold (calibration-fold Firm A cosine P5). - Computed 0.945 Firm A rate exactly (94.52%) instead of interpolated. - Fixed Ref [24] Qwen2.5-VL to full IEEE format (arXiv:2502.13923). ## New artifacts - Script 20: accountant-level three-method threshold analysis - Script 21: expanded validation (inter-CPA anchor, held-out Firm A 70/30) - paper/codex_review_gpt54_v3.md: preserved review feedback Output: Paper_A_IEEE_Access_Draft_v3.docx (391 KB, rebuilt from v3.1 markdown sources). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
17 lines
2.6 KiB
Markdown
17 lines
2.6 KiB
Markdown
# Abstract
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Regulations in many jurisdictions require Certified Public Accountants (CPAs) to attest to each audit report they certify, typically by affixing a signature or seal.
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However, the digitization of financial reporting makes it straightforward to reuse a stored signature image across multiple reports---whether by administrative stamping or firm-level electronic signing systems---potentially undermining the intent of individualized attestation.
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Unlike signature forgery, where an impostor imitates another person's handwriting, *non-hand-signed* reproduction involves the legitimate signer's own stored signature image being reproduced on each report, a practice that is visually invisible to report users and infeasible to audit at scale through manual inspection.
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We present an end-to-end AI pipeline that automatically detects non-hand-signed auditor signatures in financial audit reports.
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The pipeline integrates a Vision-Language Model for signature page identification, YOLOv11 for signature region detection, and ResNet-50 for deep feature extraction, followed by a dual-descriptor verification combining cosine similarity of deep embeddings with difference hashing (dHash).
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For threshold determination we apply three methodologically distinct methods---Kernel Density antimode with a Hartigan unimodality test, Burgstahler-Dichev/McCrary discontinuity, and EM-fitted Beta mixtures with a logit-Gaussian robustness check---at both the signature level and the accountant level.
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Applied to 90,282 audit reports filed in Taiwan over 2013--2023 (182,328 signatures from 758 CPAs) the three methods reveal an informative asymmetry: signature-level similarity forms a continuous quality spectrum that no two-component mixture cleanly separates, while accountant-level aggregates are clustered into three recognizable groups (BIC-best $K = 3$) with the three 1D methods converging within $\sim$0.006 of each other at cosine $\approx 0.975$.
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A major Big-4 firm is used as a *replication-dominated* (not pure) calibration anchor, with interview and visual evidence supporting majority non-hand-signing and a minority of hand-signers; we break the circularity of using the same firm for calibration and validation by a 70/30 CPA-level held-out fold.
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Validation against 310 byte-identical positive signatures and a $\sim$50,000-pair inter-CPA negative anchor yields FAR $\leq$ 0.001 with Wilson 95% confidence intervals at all accountant-level thresholds.
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To our knowledge, this represents the largest-scale forensic analysis of auditor signature authenticity reported in the literature.
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