Antitrust Radar
Public Data NotesAR-DN-2026-01

Where Public Market-Share Data Runs Out

Why incomplete profiles are part of the product

By Antitrust Radar Research TeamData noteMay 16, 2026Version 1.0 · Current edition

Central finding

Incomplete profiles are not failures of the platform; they are a core credibility feature.

Descriptive concentration measures do not by themselves establish competitive harm, unlawful conduct, or a causal effect.

2
sources
2
disclosure gaps
2 / 2
HHI withheld

Publication accountability

Recorded source access / review
. This is not an independent review date.
Authorship and responsibility
Antitrust Radar Research Team. Inspect individual roles and disclosure gaps.
Evidence overview

Public disclosure route

Two disclosure failures require two different public releases.

Airline named-share rows

Audit 91% named coverage and the 9% residual

Open evidence

PBM aggregate record

Preserve grouped facts without assigning shares

Open evidence

Evidence standard

Apply the publish-or-withhold calculation gate

Open evidence
Sources, citations, and policy proposals

Public action docket

What government can require next

3 asks

ForData publishers, oversight committees, and public advocates

  1. 01
    Stop hiding concentration inside aggregates

    Separate named firms from Other rows wherever disclosure rules allow, and label residual categories that cannot support HHI.

  2. 02
    Release machine-readable market tables

    Publish CSV or API tables alongside reports so readers can reproduce HHI, CR4, and source-status labels.

  3. 03
    Fund public data maintenance

    Treat competition datasets as economic infrastructure, not one-off report appendices.

Evidence still needed

Named firm sharesResidual-row policyDownloadable tables
Open advocacy brief

Reader packet

Reusable

Canonical citation

Antitrust Radar Research Team. (2026, May 16). Where Public Market-Share Data Runs Out: Why incomplete profiles are part of the product. Public Data Notes, AR-DN-2026-01 (Version 1.0). Antitrust Radar. https://antitrustradar.org/reports/public-data-gaps

JSONCSV
BibTeXRIS

Briefing packetdiagnose, specify, actGap observations JSON2 withheld HHI recordsAvailable shares CSV10 named rows + 1 residualSource registerBTS and FTC custodyAirline disclosure gap91% named / 9% aggregatePBM disclosure gapaggregate facts / 0 share rowsEvidence standardpublish-or-withhold ruleDisclosure action briefminimum public release

Source basis

BTS public airline market-share table and FTC PBM interim staff report materials.

2

Source records

2

Disclosure gaps

2

public dataset, agency report

Source types

4

Evidence asks

Read the briefing

Evidence index

Claim to public action

Published May 16, 2026 · sources through May 16, 2026 · version 1.0 · Current edition

Read / Briefing claim

Start with the authored claim and its analytical boundary.

Start with the airline residual, the PBM aggregate-only boundary, and the minimum public release specification.

Interpretation boundaryRead the finding with the report's declared market, geography, vintage, and limitations.
Read the analysis

Public Data Notes / AR-DN-2026-01

Public disclosure determines what competition analysis can prove.

Inspect two distinct failure modes, follow every available row, and turn a withheld metric into a concrete government release specification.
Exact HHI
2 / 2 withheld
no invented firm distributions
Named share rows
10
all belong to the airline screen
Aggregated residual
9%
one Other row blocks exact HHI
Official records
6
context exists even when shares do not

Disclosure workbench

Two withheld HHIs, for materially different reasons.

Switch markets to inspect the evidence boundary
01 / Residual aggregation

U.S. domestic airline passengers

Named shares plus an aggregated residual

Exact HHI withheld
Published passenger-share table91% named / 9% aggregate
2026 rolling period
Exact public share rows
Carrier rowShareStatus
Delta Air Lines17.8%Named firm
American Airlines17.5%Named firm
Southwest Airlines17%Named firm
United Airlines16.7%Named firm
Alaska Airlines6.3%Named firm
JetBlue Airways4.5%Named firm
Frontier Airlines3.7%Named firm
Spirit Airlines3.3%Named firm
SkyWest Airlines2.6%Named firm
Hawaiian Airlines1.6%Named firm
Other airlines9%Multiple firms
Measurement
Carrier share of domestic scheduled passengers
Denominator
Passengers reported in the BTS domestic market-share table for the 12 months ending February 2026
Geography
United States domestic itineraries
Source custody
Bureau of Transportation Statistics / high confidence

Disclosure requirements

“Incomplete” is a diagnosis with specific missing fields.

Available / partial / missing
Release requirementDomestic airlinesPBMs
Named firm shares
Partial10 carriers / 91% of the table
MissingNo individual PBM shares in the public record
Residual treatment
Missing9% remains inside one Other row
MissingNo participant table exists to evaluate residuals
Denominator and period
AvailableDomestic passenger shares / rolling national period
Partial2023 prescription volume is public; participant basis is not
Ownership and control
MissingSource rows do not resolve common control
MissingVertical and common-control links are not structured as shares
Stable release cadence
PartialOne current rolling-period snapshot
MissingOne aggregate 2023 concentration snapshot
Machine-readable release
PartialObservatory API available; source remains a web table
MissingNo firm-share table is available for reuse

Minimum public release

A machine-readable disclosure should make the calculation reproducible without guesswork.

6 fields
01
RequiredStable firm identifier

Join shares across releases and common-control changes.

02
RequiredFirm-level share

Reproduce HHI and top-firm structure without inference.

03
RequiredResidual-row rule

Explain every Other, suppressed, or confidential category.

04
RequiredProduct and geography

Keep each denominator and market boundary explicit.

05
RequiredOwnership and control

Aggregate firms under the economically relevant controller.

06
SupportingRelease date and revision

Maintain a reproducible cadence and correction history.

Public data is competition infrastructure.Agencies should publish stable tables, revision histories, and residual rules alongside every concentration claim.
Open the disclosure action brief

Interpretation boundary

Withholding a metric preserves the difference between evidence and inference.

A disclosure gap is an evidence finding, not proof of low or high concentration. Named-firm subtotals, aggregate top-firm facts, residual shares, market definitions, and enforcement records answer different questions. Antitrust Radar publishes each layer separately and withholds HHI whenever the public record does not close a firm-level distribution under a defensible denominator and control structure.
Read the full evidence standard

Executive summary

Incomplete profiles are not failures of the platform; they are a core credibility feature. The airline profile shows a high-quality BTS source but withholds HHI because the public table includes an aggregated Other category. The PBM profile uses FTC public findings on top-three and top-six concentration but withholds HHI because individual public shares are not provided in the press-release record. The observatory publishes what is known, what is missing, and what source would be needed next.

2 / 2

market HHIs correctly withheld

The airline and PBM records fail different firm-level disclosure requirements; neither is converted into an invented score.

Public evidence gate

10

named airline share rows

The rows cover 91 percent of the passenger-share table and support CR4, but not an exact full-market HHI.

BTS TranStats

9%

aggregated airline residual

The Other row can be published as a gap, but its hidden firm distribution cannot be assigned a squared-share contribution.

Residual-row boundary

6

linked official records

Policy context remains available even while the market-share evidence needed for HHI is incomplete.

Official evidence custody

Research map

What this briefing connects

  • Why HHI is withheld
  • Examples from airlines and PBMs
  • What better source coverage would add

Source basis

BTS public airline market-share table and FTC PBM interim staff report materials.

Bounded disclosure evidence

Reuse what is published; specify what government must release next.

Airline residual dossier

Ten named rows, one unresolved Other category

Open evidence

PBM aggregate-only dossier

Grouped FTC facts with zero named share rows

Open evidence

Official source register

Audit BTS and FTC custody before reuse

Open evidence

Methodology and limits matter

A disclosure gap is an evidence finding, not proof of low or high concentration. Named-firm subtotals, aggregate top-firm facts, residual shares, market definitions, and enforcement records answer different questions. Antitrust Radar publishes each layer separately and withholds HHI whenever the public record does not close a firm-level distribution under a defensible denominator and control structure.

Source basis

BTS public airline market-share table and FTC PBM interim staff report materials.

Source register

2 cited public records

01 / 2
public dataset2026

Source 01

TranStats airline domestic market share March 2025-February 2026

Bureau of Transportation Statistics

Bureau of Transportation Statistics TranStats, Airline Domestic Market Share, March 2025-February 2026.

BTS TranStats homepage reporting domestic airline market share for the 12 months ending February 2026.

Accessed
May 16, 2026
Custody
Public federal government dataset

Related reports

The U.S. Competition Landscape

Research actions

Audit BTS share tableAudit FTC PBM recordView disclosure standard
Public action memoImmediate

What public institutions should do next

Data gaps are not a footnote; they are the place where public accountability breaks down and private market power becomes harder to challenge.

Audience

Data publishers, oversight committees, and public advocates

1Stop hiding concentration inside aggregatesSeparate named firms from Other rows wherever disclosure rules allow, and label residual categories that cannot support HHI.
2Release machine-readable market tablesPublish CSV or API tables alongside reports so readers can reproduce HHI, CR4, and source-status labels.
3Fund public data maintenanceTreat competition datasets as economic infrastructure, not one-off report appendices.
Evidence needed
Named firm sharesResidual-row policyDownloadable tablesData update cadence
Connect to advocacy playbooks

Policy claims are framed as public-interest asks, not legal conclusions. Each ask should be read with the report’s source basis and limitations.