REVIEW 5 major objections 8 minor 14 references
InvestAlign: Overcoming Data Scarcity in Aligning Large Language Models with Investor Decision-Making Processes under Herd Behavior
T0 review · 5 major / 8 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read The paper argues that synthetic data from a solvable investment model can replace scarce real-user data when aligning language models to human investors.
desk verdict A practical empirical alignment result that leans on a shaky theoretical convergence proof; the 44–61% MSE reductions are real, but Eq. 28 needs either a proper proof or a demotion to observation. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The engine is P3's closed-form optimal decision rule, Eq. (11), which expresses A1's optimal investment $\hat{P}_1(t)$ as a function of risk-aversion coefficients $\alpha_1, \alpha_2$, influence coefficient $\theta_1$, market parameters $r, v, \sigma$, and a numerically computed constant $\eta$. The paper uses this rule to generate $10^3$ training samples over varied investment attributes. The convergence argument compares cross-entropy gradient norms for theoretical versus real-user data; assuming real-user decisions equal the theoretical solution plus i.i.d. uniform noise, the theoretical-data loss has a larger gradient norm, which in a locally convex loss landscape implies faster parameter convergence.
What would settle it
Using the paper's collected P3 data, compute the residuals $\tilde{P}_1^i(t) - \hat{P}_1^i(t)$ for each participant and time step; if they are visibly non-uniform, serially correlated, or shifted away from zero, the assumed noise model in Section 4.2 is violated, and one can directly test whether the theoretical-data gradient norm still exceeds the real-data gradient norm when the empirical residual distribution is used instead of $U(-\varepsilon, \varepsilon)$.
Extended reading notes
Core claim
The central claim is that supervised fine-tuning on SFT datasets built from the closed-form solution of the simple problem P3 (absolute herd behavior with unilateral influence) produces InvestAgents whose investment decisions align with real-user decisions better than models before fine-tuning, in P3 and also in the complex problems P1 (relative herd behavior, unilateral influence) and P2 (absolute herd behavior, mutual influence). Across the tested models, the paper reports overall mean squared error reductions of 45.59–61.26% for P3, 44.52–56.69% for P1, and 45.77–60.92% for P2 relative to the unfine-tuned baselines. The faster-convergence claim is stated as the gradient-norm inequality $\|\nabla \hat{L}(w)\| > \|\nabla \tilde{L}(w)\|$ in Eq. (28), and is supported by measured gradient norms and training-loss curves.
Load-bearing premise
The proof assumes that real people's investment decisions are the mathematically optimal solution plus independent random noise spread evenly within fixed bounds, and that the range of possible human choices fits inside the range the model can produce; if human decisions contain systematic biases that the optimal-investment-plus-herding model does not capture, the faster-convergence inequality and the alignment benefit do not follow.
Editorial extensions
If this is right
- If correct, LLM-based investment agents can be aligned to herd-affected human decision-making without collecting large proprietary datasets of individual investment choices.
- The same recipe—solve a simple solvable analog, generate SFT samples, fine-tune—could in principle be applied to other decision problems in behavioral finance where stylized closed-form solutions exist.
- Theoretical-data fine-tuning should be preferred to real-user data when the theoretical model is a good proxy, because it converges faster; adding a smaller amount of real-user data can further reduce error.
- The trained InvestAgents reproduce two economic hypotheses: investment decisions converge as herd influence increases, and stronger mutual influence lowers expected total terminal wealth.
- Fine-tuning on a general financial-domain dataset performs worse on this task than fine-tuning on the theoretically generated herd-behavior dataset.
Reading between the lines
- (Editorial inference) The faster-convergence proof relies on the idealization that human noise is uniform and independent; a natural next test is whether inequality (28) still holds when residuals are skewed, heteroskedastic, or autocorrelated.
- (Editorial inference) The method's usefulness will be governed by how far a solvable toy problem can deviate from the target problem before the learned behavior stops transferring; comparing InvestAlign against a model fine-tuned on a size-matched random sample of real-user data would sharpen this.
- (Editorial inference) Extending the approach to other behavioral biases such as loss aversion or overconfidence would require closed-form solutions of the same style for those biases, or a hybrid dataset blending theory with a thin layer of real data.
- (Editorial inference) Because the paper measures alignment as closeness to the average human decision, a complementary test would be whether InvestAgent reproduces the full distribution of human choices, including the spread and individual heterogeneity, not just the mean.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper proposes InvestAlign, a framework for data-scarce supervised fine-tuning (SFT) of LLMs in behavioral finance. Given a complex optimal investment problem, InvestAlign identifies a similar and simple problem (P3: absolute herd behavior with unilateral influence) whose closed-form theoretical solution (Eq. (11), from the authors' prior work) is used to generate synthetic SFT datasets, and fine-tunes base LLMs (GPT-3.5, Qwen-2, Llama-3.1, GLM-4) into 'InvestAgents.' The paper reports that (i) the theoretical P3 solution is statistically consistent with decisions collected from 119 human participants (Section 3.3, Appendix A.6); (ii) InvestAgents reduce overall MSE relative to pre-SFT LLMs by 44–61% on P3 and on the complex problems P1 (relative herd, unilateral influence) and P2 (absolute herd, mutual influence) (Table 1); and (iii) fine-tuning on theoretical data yields faster parameter convergence than fine-tuning on real-user data, supported by a gradient-norm inequality (Eq. (28)) and by experiments in Figures 3–4. The paper also includes ablations, FinGPT baselines, mixed-data robustness checks, and validation of economic hypotheses H1/H2.
Significance. The empirical alignment results, if they hold up, are valuable: they offer a concrete, reproducible route to LLM alignment in a domain where real-user data are costly and privacy-sensitive, and they demonstrate genuine transfer from a solvable proxy problem to harder problems. The paper ships public code, reports consistent MSE reductions across three base models and three problems, and includes several substantiating analyses (hyperparameter ablations in A.9, FinGPT baselines in A.11, mixed-data robustness in A.10, and economic-principle checks in A.12) that go beyond a single headline number. The theoretical faster-convergence claim is the paper's weakest component: the proof of Eqs. (27)–(28) is a one-line assertion that is demonstrably invalid, and the noise model on which it rests is unvalidated. The observed gradient-norm difference in Figures 3–4 may still hold empirically in the tested settings, but it does not establish the advertised theorem.
major comments (5)
- [§4.2 / Appendix A.8, Eqs. (27)–(28)] The claimed proof of the faster-convergence result is invalid. The paper asserts that 'Because f_P1(t)(·) is monotonically decreasing, from (7) and (21), we can prove that Î < Ĩ < 1', but monotonicity of the model density does not determine the comparison of the two overlap integrals Î = ∫_{P̂} f̂ f_model dx and Ĩ = ∫_{P̃} f̃ f_model dx. A discrete counterexample that satisfies all of the paper's assumptions (f̂ decreasing, f̃ = f̂ convolved with symmetric uniform noise, f_model decreasing, supports nested with P̂ ⊂ P̃) is: f̂ on {1,2} with probabilities (0.8, 0.2); noise n ~ U(−1,1) so f̃ on {0,1,2,3} has probabilities (4/15, 1/3, 1/3, 1/15); f_model on {0,1,2,3} = (0.3, 0.3, 0.2, 0.2). Then Î = 0.8·0.3 + 0.2·0.2 = 0.28 > Ĩ = 4/15·0.3 + 1/3·0.3 + 1/3·0.2 + 1/15·0.2 = 0.26, which by the paper's own Eqs. (22)–(23) gives ||∇Lhat(w)|| < ||∇Ltilde(w)||, the reverse of Eq. (28). The faster-convergence theorem is therefore not established even under the paper's stated assumptions; the empirical evidence in Figures 3–4 is a separate matter.
- [§4.2] The convergence analysis rests on assumptions that are neither validated against the collected data nor stated with their evidentiary status: (i) real-user decisions equal the theoretical optimal solution plus i.i.d. U(−ε, ε) noise, with ε never estimated from the 119 participants' data; (ii) the support nesting P̂1(t) ⊂ P̃1(t) ⊂ P1(t); (iii) monotonicity of the LLM output density f_P1(t)(·); and (iv) the constancy of η when α1 and θ1 vary slightly (Appendix A.7). Under assumption (i), the comparison in Eq. (28) is between a clean signal and the same signal corrupted by noise, so the conclusion is substantially entailed by the modelling choice rather than by a property of investor behavior. The statistical validation in Section 3.3 and Appendix A.6 (difference t = −1.075; correlation t = −0.843 against 0.85) tests only whether the theoretical solution is close to real-user data in mean and correlation; it does not test the uniform-noise, independence, support-nesting, or monotonicity assumptions. The paper should either validate these assumptions empirically or re-frame the convergence claim as an empirical observation.
- [§4.2, Figures 3–4] The empirical comparison of gradient norms is confounded by a dataset-size and coverage mismatch. The theoretical SFT dataset contains 10³ samples (10 α1 values × 10 θ1 values × 10 trials) with uniform attribute coverage, whereas the real-user SFT dataset contains at most 119 samples concentrated in a few attribute classes (Section 3.2). The paper's second assumption ('sample size sufficiently large') is therefore false for the real-user dataset. The observed higher gradient norm on theoretical data could be due to the larger, more uniformly covered dataset rather than to the absence of label noise. A matched-sample comparison (e.g., subsampling the theoretical dataset to match the real-user class distribution and size, or upsampling the real-user data) is needed to support the convergence-rate claim.
- [§5.2, Table 1 (P2 rows)] The reported overall MSE for P2 is computed over the union P2 ∪ P3, not over the P2 data alone. Because P3 is exactly the problem on which InvestAgents were fine-tuned, including P3 data in the P2 metric can inflate the apparent cross-task improvement, and the statement that InvestAlign 'reduce[s] the overall MSEs by ... in P2' is not supported by a P2-only measurement. The authors should report the MSE restricted to the 44 P2 participants (or to the attribute classes actually covered by them) and clarify why the union was used.
- [§5.1, Table 1 and Abstract] The headline claim of 'significantly closer alignment' is supported only by point estimates of overall MSE reductions (45.59%–61.26%), with no confidence intervals or significance tests. Since the real-user samples are small (119, 80, and 44 participants for P3, P1, and P2) and the LLM responses are averaged over 10 seeds, bootstrap confidence intervals on the MSE reductions or a paired test over attribute classes should be reported to justify the word 'significantly'.
minor comments (8)
- [Appendix A.6] The null hypothesis 'mean correlation coefficient does not differ from 0.85' (t-statistic −0.843) uses a threshold (0.85) whose justification is not given; reporting the estimated mean and confidence interval of {ρi} would be more informative.
- [§5.2, Table 1] The text says GPT-3.5 was also evaluated on P2, but Table 1 contains no GPT-3.5 row for P2; the discrepancy should be resolved.
- [§5.1, Eqs. (9)–(10)] The overall MSE averages over attribute classes without weighting by the number of participants in each class, so classes with a single participant count as much as classes with many; a participant-weighted average or a per-class coverage report would be more robust.
- [§3.1] The symbol T denotes both the time horizon and the time set T = [0, T], and in Eqs. (6) and (26) P1(t) is used for both the decision variable and its support range; distinct notation would remove ambiguity.
- [Appendix A.4] GLM-4 results are shown in Figure 6 but no GLM-4 entries appear in Table 1; adding them would let readers compare all four models on the same metric.
- [§4.2, Eq. (21)] The derivation of Eq. (21) identifies f_P1(t)(x) with Sigmoid(z) without defining the mapping from the decision value x to the sigmoid input z; this step needs an explicit statement.
- [Appendix A.5] The section heading 'Comparison of Real-User Data and Pre-SFT LLMs' Investment Decision on P1 and P1' appears to contain a typo; it should likely read 'P1 and P2'.
- [§4.2, citation (Chen and Xiang, 2018)] The claim that 'a larger gradient norm leads to faster convergence' cites a survey of unstable gradients; this is a heuristic rather than a convergence-rate theorem, and even if Eq. (28) were valid, additional assumptions on the loss landscape would be needed to conclude a faster convergence rate.
Circularity Check
The advertised faster-convergence theorem is tautological: real-user data are defined as the theoretical solution plus noise, so the proof compares the theory with a noisy copy of itself; the empirical alignment results remain independently tested.
-
self definitional
[Section 4.2, Eqs. (26)-(28)]
"Because the real-user data often have a bigger noise than the theoretical solution, we assume that P̃1(t) is P̂1(t) plus a white noise n(t) that independently and identically satisfies a uniform distribution U(−ε, ε), i.e, P̃1(t) = P̂1(t) + n(t). ... Because the investment decisions of the pre-SFT LLM can be arbitrary due to the randomness of model parameters, we have P̂1(t) ⊂ P̃1(t) ⊂ P1(t). Because fP1(t)(·) is monotonically decreasing, from (7) and (21), we can prove that Î < Ĩ < 1, and thus we have ∥∇L̂(w)∥ > ∥∇L̃(w)∥."
The faster-convergence result compares the theoretical density f̂ with a target f̃ that is, by the paper's own construction, the convolution of f̂ with U(−ε,ε). 'Real-user data' is thereby defined as a noisy copy of the very theoretical solution whose superiority is being proved. The theorem therefore reduces to the tautology that a clean signal has a larger gradient norm than its own smoothed version; no property of the actually collected real-user distribution enters the proof. The conclusion is entailed by the definition of the comparator rather than by the data. The asserted inequality Î<Ĩ is also not implied by monotonicity of f_model alone, but that is a mathematical-validity issue distinct from the circularity.
full rationale
InvestAlign's empirical alignment claims are not circular: the SFT dataset is generated from the closed-form solution (11) cited to Wang and Zhao 2024b, and the alignment of InvestAgents with real-user decisions in P3, P1, and P2 is measured against separately collected questionnaire data using overall MSE. No parameter of the theoretical solution is fitted to those test data, and the P1/P2 evaluations use held-out complex-problem data, so those results have independent empirical content. The structural circularity is confined to the theoretical faster-convergence result advertised in the abstract and Section 4.2. There, the paper explicitly models real-user investment decisions as the theoretical optimal decision plus uniform noise, then 'proves' that training on the theoretical solution converges faster. That is not a comparison against independent real-user behavior; it is a comparison between a distribution and its own noise-smoothed version, so the advertised advantage is built into the input model. In addition, the key step Î<Ĩ in Eq. (27) does not follow from the stated monotonicity and nesting assumptions and can fail, which further weakens the proof independently of circularity. The self-citations to the authors' prior work supply the P3 solution and the η≈constant approximation; these are prior stated-assumption results rather than circular renaming, though they are load-bearing. The experimental gradient-norm and training-loss comparisons using actual real-user data provide some independent empirical support for the convergence claim, which is why the circularity is partial rather than total.
Assumptions & free parameters
free parameters (2)
- Noise bound epsilon in real-user model =
unspecified
- Attribute ranges Salpha1 and Stheta1 =
[0.09,0.38] and [0,1e-7]
assumptions (5)
- domain assumption The Merton-style optimal investment model with exponential utility and herding penalty (Eq. 2) describes real investor decision-making.
- ad hoc to paper Real-user decisions equal the theoretical optimal solution plus i.i.d. uniform noise.
- ad hoc to paper The LLM output layer is a Sigmoid and the SFT loss is a continuous cross-entropy between densities of investment decisions.
- ad hoc to paper The supports nest as P1hat(t) subset P1tilde(t) subset P1(t), and the model density f_P1(t) is monotonically decreasing.
- ad hoc to paper The parameter eta in Eq. (11) remains approximately constant when alpha1 and theta1 vary slightly.
Cite this review
Pith. "Pith review of InvestAlign: Overcoming Data Scarcity in Aligning Large Language Models with Investor Decision-Making Processes under Herd Behavior." pith.science (2026). https://pith.science/paper/V6MY3UX7
@misc{pith2026250706528,
author = {Pith},
title = {Pith review of: InvestAlign: Overcoming Data Scarcity in Aligning Large Language Models with Investor Decision-Making Processes under Herd Behavior},
year = {2026},
howpublished = {\url{https://pith.science/paper/V6MY3UX7}},
note = {Machine review of arXiv:2507.06528}
}
read the original abstract
Aligning Large Language Models (LLMs) with investor decision-making processes under herd behavior is a critical challenge in behavioral finance, which grapples with a fundamental limitation: the scarcity of real-user data needed for Supervised Fine-Tuning (SFT). While SFT can bridge the gap between LLM outputs and human behavioral patterns, its reliance on massive authentic data imposes substantial collection costs and privacy risks. We propose InvestAlign, a novel framework that constructs high-quality SFT datasets by leveraging theoretical solutions to similar and simple optimal investment problems rather than complex scenarios. Our theoretical analysis demonstrates that training LLMs with InvestAlign-generated data achieves faster parameter convergence than using real-user data, suggesting superior learning efficiency. Furthermore, we develop InvestAgent, an LLM agent fine-tuned with InvestAlign, which demonstrates significantly closer alignment to real-user data than pre-SFT models in both simple and complex investment problems. This highlights our proposed InvestAlign as a promising approach with the potential to address complex optimal investment problems and align LLMs with investor decision-making processes under herd behavior. Our code is publicly available at https://github.com/thu-social-network-research-group/InvestAlign.
Figures
Figures from the paper (15 more)
Reference graph
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Reviewed August 6, 2026 · model on record in the stance chip above.
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