arxiv: 2604.10194 · v1 · submitted 2026-04-11 · 💱 q-fin.TR · q-fin.MF

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Mandatory Disclosure in Oligopolistic Market Making

Seongjin Kim , Jin Hyuk Choi

Authors on Pith no claims yet

Pith reviewed 2026-05-10 16:08 UTC · model grok-4.3

classification 💱 q-fin.TR q-fin.MF

keywords mandatory disclosuremarket makingoligopolyliquidityprice impacttrading costsSarbanes-Oxley Actdifference-in-differences

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The pith

Mandatory disclosure reduces trading costs more when market makers compete less.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper builds a multi-period model of informed trading where market makers compete imperfectly and informed traders must disclose their positions. It shows that requiring disclosure leads to lower price impact from trades, cutting costs for uninformed traders. This liquidity benefit is larger when fewer market makers are active. The model proves a unique linear equilibrium exists under these rules. Data from the 2002 Sarbanes-Oxley disclosure changes confirm that stocks with less competition saw greater spread reductions.

Core claim

In a multi-period Kyle-type model incorporating mandatory disclosure of informed trades and imperfect competition among market makers, a unique linear equilibrium exists. Disclosure enhances liquidity by reducing the price impact of trades, with its marginal benefit strictly larger when competition among market makers is weak. This prediction is confirmed empirically using the 2002 Sarbanes-Oxley Act as a natural experiment, where difference-in-differences analysis shows larger spread reductions for stocks with fewer active market makers.

What carries the argument

The linear equilibrium of the multi-period model with mandatory disclosure and oligopolistic market making, which links the degree of competition to the liquidity benefits of disclosure through reduced price impact.

Load-bearing premise

The model assumes that a linear equilibrium exists and is unique under the combination of mandatory disclosure and oligopolistic market making, and that the 2002 Sarbanes-Oxley Act serves as a clean natural experiment isolating disclosure effects.

What would settle it

A finding that spread reductions after the disclosure reform were not larger for low-competition stocks, or the existence of non-linear equilibria in the model, would contradict the central claim.

Figures

Figures reproduced from arXiv: 2604.10194 by Jin Hyuk Choi, Seongjin Kim.

**Figure 1.** Figure 1: Estimated effect of SOX Section 403 on log(Spread) as a function of market maker count. The solid curve plots βˆ1 +βˆ3 ×log(1 +MMCNT) using estimates from [PITH_FULL_IMAGE:figures/full_fig_p009_1.png] view at source ↗

read the original abstract

We develop a multi-period Kyle-type model that incorporates both mandatory disclosure of informed trades and imperfect competition among market makers. We prove the existence and uniqueness of a linear equilibrium and show that the liquidity-enhancing effect of disclosure is fundamentally linked to the degree of market-making competition. Disclosure lowers trading costs by reducing price impact, and its marginal benefit is strictly larger when competition is weak. We empirically validate this prediction using the 2002 Sarbanes-Oxley Act disclosure reform as a natural experiment. A difference-in-differences analysis of U.S. equities confirms that the spread reduction following enhanced disclosure is significantly larger for stocks with fewer active market makers.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper shows disclosure cuts liquidity costs more under weak market-maker competition in an extended Kyle model, with a matching SOX DiD, but the empirical identification looks vulnerable to confounding.

read the letter

The main things to take away are that they extend a multi-period Kyle setup to include mandatory disclosure of informed trades plus oligopolistic market makers, prove a unique linear equilibrium exists, and show the liquidity gain from disclosure is larger when competition is thin. They then test the prediction with a difference-in-differences around the 2002 SOX reform and find bigger spread reductions for stocks that had fewer active market makers beforehand. That combination of theory and empirical pattern is the core contribution. The model work is clean on its own terms. Adding disclosure and imperfect competition among makers, then deriving the equilibrium and the comparative static on competition intensity, gives a clear mechanism that prior Kyle papers did not have. The proof of existence and uniqueness is stated directly, which is the right standard for this style of model. The empirical piece lines up with the theory at first glance. Using an external regulatory event rather than fitting parameters is the right approach, and splitting by pre-existing competition intensity is a natural way to test the mechanism. The soft spot is the DiD identification. SOX bundled disclosure changes with internal-control mandates, governance rules, and auditor requirements whose costs and effects on spreads vary with firm size, complexity, and liquidity. Those factors also correlate with the number of market makers, so the parallel-trends assumption is not obviously safe without further checks. The abstract gives no detail on how they handle that or on robustness to alternative competition measures. This paper is for microstructure researchers and anyone thinking about how disclosure rules interact with venue competition. A reader who wants a mechanism linking the two would get value from the model even if the empirics need more work. It deserves peer review because the theoretical result is grounded and the question is policy-relevant; referees can focus on whether the DiD holds up once the other SOX channels are addressed.

Referee Report

2 major / 2 minor

Summary. The paper develops a multi-period Kyle-type model with mandatory disclosure of informed trades and oligopolistic market making. It proves existence and uniqueness of a linear equilibrium, shows that disclosure reduces price impact and trading costs with the marginal liquidity benefit strictly larger under weaker competition, and empirically validates this via a DiD analysis around the 2002 Sarbanes-Oxley Act, finding larger post-reform spread reductions for stocks with fewer active market makers.

Significance. If the equilibrium characterization and comparative statics hold, the paper makes a useful contribution by formally linking disclosure policy to the degree of market-maker competition in determining liquidity outcomes. The proof of linear equilibrium existence/uniqueness under these primitives is a clear strength, as is the attempt to test the model's key prediction with a regulatory event. The result has potential policy relevance for disclosure rules in concentrated dealer markets, though its overall impact depends on resolving identification concerns in the empirical component.

major comments (2)

[§5] §5 (Empirical Analysis), DiD specification: The central empirical claim that disclosure's liquidity benefit is larger under weak competition rests on the interaction term in the DiD around SOX 2002. However, SOX bundled disclosure changes with other provisions (Section 404 internal controls, auditor independence, governance reforms) whose compliance costs and spread effects are known to vary with firm size, complexity, and liquidity—variables correlated with the number of active market makers. No robustness checks, additional controls, or evidence on parallel trends after netting out these channels are described, which is load-bearing for validating the model's prediction.
[§3.2] §3.2, equilibrium derivation: The proof of existence and uniqueness of the linear equilibrium under mandatory disclosure assumes a specific information structure and multi-period updating; the paper should explicitly verify that the price-impact expression (and resulting comparative statics on competition) remains valid when the disclosure reveals the informed trader's position each period, as any implicit restriction on the market makers' filtering could affect the claim that marginal benefits are strictly larger when competition is weak.

minor comments (2)

The abstract and introduction could more precisely state the sample period, number of stocks, and exact definition of 'active market makers' used in the empirical exercise.
Notation for the number of market makers (e.g., N) and the disclosure parameter should be introduced earlier and used consistently in the model section to improve readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on our manuscript. We address each major comment below and indicate where revisions will be made to strengthen the paper.

read point-by-point responses

Referee: §5 (Empirical Analysis), DiD specification: The central empirical claim that disclosure's liquidity benefit is larger under weak competition rests on the interaction term in the DiD around SOX 2002. However, SOX bundled disclosure changes with other provisions (Section 404 internal controls, auditor independence, governance reforms) whose compliance costs and spread effects are known to vary with firm size, complexity, and liquidity—variables correlated with the number of active market makers. No robustness checks, additional controls, or evidence on parallel trends after netting out these channels are described, which is load-bearing for validating the model's prediction.

Authors: We acknowledge that SOX encompasses multiple provisions beyond disclosure, and that their effects may correlate with firm characteristics linked to market-maker competition. Our DiD exploits cross-sectional variation in the number of active market makers to test the model's specific prediction on differential liquidity benefits. To address potential confounding, we will add robustness specifications that include additional controls for firm size, complexity, and liquidity, along with parallel-trends tests that net out these channels. We will also expand the discussion of identification limitations in the revised empirical section. revision: yes
Referee: §3.2, equilibrium derivation: The proof of existence and uniqueness of the linear equilibrium under mandatory disclosure assumes a specific information structure and multi-period updating; the paper should explicitly verify that the price-impact expression (and resulting comparative statics on competition) remains valid when the disclosure reveals the informed trader's position each period, as any implicit restriction on the market makers' filtering could affect the claim that marginal benefits are strictly larger when competition is weak.

Authors: The multi-period equilibrium derivation already incorporates full revelation of the informed trader's position each period, with market makers updating beliefs on the basis of both order flow and the disclosed trades. The linear price-impact coefficient is obtained from the resulting filtering problem and the resulting comparative statics with respect to the number of market makers. We will add an explicit verification step in the revised proof of §3.2 to confirm that the expression and the strict inequality on marginal benefits under weak competition continue to hold under this information structure, with no implicit restrictions on filtering. revision: yes

Circularity Check

0 steps flagged

Derivation self-contained; no circular reductions identified

full rationale

The paper constructs a multi-period Kyle-type model with mandatory disclosure and oligopolistic market makers, then proves existence and uniqueness of a linear equilibrium directly from the stated primitives (information structure, payoff functions, and competition parameters). The claimed link between disclosure's marginal liquidity benefit and the degree of competition is obtained by solving the resulting equilibrium conditions for price impact and trading costs; this is a standard first-principles derivation rather than a re-labeling or fit. No load-bearing self-citations, ansatzes smuggled via prior work, or fitted inputs renamed as predictions appear in the theoretical chain. The empirical DiD component relies on an external regulatory event (SOX) rather than parameters estimated from the same data used to derive the prediction, keeping the theoretical result independent of its validation.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only the abstract is available; specific free parameters, axioms, and invented entities in the full model cannot be identified.

pith-pipeline@v0.9.0 · 5396 in / 1055 out tokens · 34782 ms · 2026-05-10T16:08:28.631631+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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