Professional, Scientific, and Technical Services (U.S.) — NAICS 541

A Histometrics rollup primer for a general investing audience — relevant to both public-market and private investors. Core figures are our ground-truth U.S. federal statistics; forward-looking statements are labeled as judgments. NAICS = North American Industry Classification System, the U.S. government's standard code for an industry. This page covers the subsector (3-digit) 541, which rolls up nine child industry groups (5411 through 5419). It synthesizes those nine child primers plus our federal stats for this level; it does not re-research from scratch. Current as of July 2026.

What this page adds. These nine industries share one label and one business model — sell expert judgment billed by time, not a product on a shelf — and almost nothing else. The value of reading the subsector rather than a single child is the contrast: which industries are big, which are growing, who owns them, how concentrated they are, and — the single most important axis here — whether you can invest in them at all. Public-market access does not track size, so Section 2 leads with the side-by-side. Later sections cover the subsector as a whole. For any one industry in full, follow its child primer (5411–5419).

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1. Overview

NAICS 541 is the expertise-for-hire economy: firms that get paid for the skilled labor of lawyers, accountants, engineers, designers, programmers, consultants, scientists, ad-makers, and a long tail of specialists. In the NAICS hierarchy the "Professional, Scientific, and Technical Services" sector (2-digit, code 54) contains exactly one subsector — this one, 541 — so for practical purposes 541 is the whole professional-services sector of the U.S. economy.[3]

It is enormous: roughly $2.67 trillion of receipts in 2022 across about 876,000 firms and 989,000 establishments, employing about 10.4 million people — one of the largest and highest-wage service sectors in the country.[1][2] Three structural facts define the whole subsector for an investor:

1. It is a people business, not a capital business. Payroll is about 42% of receipts (roughly $1.11 trillion of payroll against $2.67 trillion of receipts), average pay is about $107,000 per worker, and the main asset walks out the door every night.[1][2] Profit comes from billing skilled labor at a multiple of its cost.
2. It is extraordinarily fragmented — yet public access is wildly uneven. Subsector concentration is near the theoretical floor (a Herfindahl-Hirschman Index of 7.9), and no company spans it.[1] But whether you can buy a given child ranges from "deep public bench" (IT services, engineering, biotech/contract research, payroll) to "essentially un-buyable" (law firms, specialized design).
3. Private equity is the universal consolidation engine. Every child is a roll-up story — of clinics, of accounting practices, of engineering shops, of IT firms, of consulting boutiques — even as the base of each market stays atomized.

The useful mental model is not "one sector" but nine different ownership-and-access stories bolted to one taxonomy heading.

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2. What's inside — the nine children and how they differ

NAICS nests from broad to narrow: sector (2-digit) → subsector (3-digit, this page) → industry group (4-digit, the children below) → industry (5-digit) → national industry (6-digit). Subsector 541 splits into nine industry groups. Here is how they contrast on the axes an investor actually cares about, ranked by share of the subsector's 2022 receipts.[1][4]–[12]

HHI = Herfindahl-Hirschman Index, a 0–10,000 concentration gauge where U.S. antitrust agencies treat anything under ~1,500 as "unconcentrated"; CR4 = the combined revenue share of the four largest firms.[13] REIT = real estate investment trust. CRO = contract research organization. Tickers and multiples are held for Sections 4 and 10. Shares are each child's 2022 Economic Census receipts as a percentage of the subsector's $2,667.3 billion.

The four contrasts that matter most:

1. Size is spread, not concentrated in one child. Unlike a typical rollup where one industry dominates, 541's revenue is genuinely distributed: the top three children (IT services, consulting, engineering) are each 15–22% and together are just over half; even the ninth (specialized design) is a real $37-billion industry. This is nine substantial economies, not a whale-and-minnows.

2. Public access is inverse to intuition — and it is the whole investment story. The taxonomy tells you nothing about how to buy in. Legal Services is the fourth-largest child (~14%) yet is nearly un-investable directly, because U.S. law firms cannot be owned by non-lawyers.[4] Specialized Design and most of "Other" (veterinary clinics, translation, polling) have no listed pure-play at all. Meanwhile the cleanest public benches sit in engineering, IT services, payroll (a slice of accounting), and biotech/contract research (a slice of R&D). Reading at this level tells you where the listed exposure actually lives versus where the money is.

3. Concentration runs opposite to size, and the leaders never span children. The smallest, most specialized children can be the more concentrated ones (accounting at HHI 300 because of the Big Four; advertising at 79 because of the holding companies), while giant children like Legal (10.3) and Engineering (19.9) are atomized. Crucially, no acquirer is large across children — the leaders of IT services are not the leaders of veterinary or title insurance.

4. The economics diverge under one label. Most children run the same billable-hours engine, but the exceptions are where the money changes character: billboards inside advertising are a real-estate/REIT business; title inside legal and testing inside engineering run on operating leverage; payroll inside accounting earns float income that rises with interest rates; biotech inside R&D lives on milestones, royalties, and cash runway; veterinary inside "Other" is a cash-pay medical business. One valuation lens does not fit all nine.

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3. How big it is (this subsector's rollup figures)

These are our ground-truth federal statistics for NAICS 541. Receipts, firm counts, and concentration come from the 2022 Economic Census (EC); establishments, employment, and payroll from 2023 County Business Patterns (CBP). The two programs use different years and methods and should not be read as one income statement.[1][2]

Derived: roughly 10.5 employees per establishment, about $3.0 million of receipts per firm, average pay near $107,000 per worker, and payroll at about 42% of receipts — the twin signatures of a very large, high-skill labor economy made of hundreds of thousands of small shops rather than a few giants.[1][2] First-quarter payroll is ~25% of the annual total, so there is no meaningful seasonality at the aggregate.

The children reconcile almost perfectly to the subsector — a genuine ground-truth cross-check. The nine children's employment sums to 10,401,442, exact to the person, and their establishments to 989,182, exact; receipts (~$2,667.3B) and annual payroll (~$1,114.5B) sum to a rounding error. Firm counts are the one line that does not add cleanly — the children total ~878,000 against the subsector's 876,176 — because a firm operating in more than one industry group is counted in each child but only once at the parent. The parts add up to the whole.[4]–[12]

The pooled subsector is more fragmented than almost every child — and that is an artifact, not a fact about competition. The subsector's HHI of 7.9 sits below eight of its nine children; the lone exception is Specialized Design (4.8), itself the most atomized pool in the sector. Pooling nine different service markets into one code mechanically dilutes concentration — a firm that leads IT services holds zero share of veterinary or title insurance, so every large firm's combined share shrinks against the bigger denominator. Read the 7.9 as confirmation that no company spans the sector, not as evidence that any individual market is frictionless. The real pricing power lives within the more concentrated children (accounting's Big Four, advertising's holding companies, the economic-consulting houses inside 5416).[1]

Undercount caveat — large, and it runs one direction: the $2.67 trillion is a floor. These are employer-firm figures, and four exclusions all push the true footprint higher, each biggest exactly where small or individual ownership dominates:

1. Nonemployers are excluded. CBP and the EC count only businesses with paid staff. Professional services is one of the largest nonemployer categories in the country — solo lawyers, freelance designers and programmers, one-person consultancies, independent appraisers, self-employed photographers and translators — none of which appear above. The true count of operators is far higher than 876,000, though because each is tiny they add more to the count than to the dollars.
2. In-house work is invisible. Vast volumes of legal, accounting, engineering, design, IT, research, and marketing work happen inside the companies that consume them and are counted in their industries — a corporate law department, a manufacturer's R&D lab, a retailer's in-house design studio, a bank's captive IT.
3. Government does much of it in-house — public-agency lawyers, engineers, scientists, and IT staff are counted nowhere here.
4. Cross-classification leaks revenue — brand-name firms spread revenue across codes (a Deloitte books strategy, tech, and HR in three different places), and offshore delivery of work for U.S. clients never lands in U.S.-establishment receipts.

Our federal file for this level carries no nonemployer, in-house, government, margin, utilization, or growth series, so none is asserted here. Treat $2.67 trillion as the reliable core of the employer segment; the total economic footprint of professional work is materially larger.

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4. Investable universe (where value concentrates across the children)

The defining fact: the public-market map does not line up with the size map. Value — for a listed investor — concentrates in only a few children, and reaches the rest only indirectly. Treat every name below as an exposure vehicle, not a clean proxy; each blends the target activity with other businesses and geographies.

• Where the deep public benches are. Four children carry most of the listed exposure. Engineering (in 5413) has the sector's deepest direct bench (AECOM, Jacobs, WSP, Stantec, Tetra Tech, Parsons, KBR, Fluor). IT services (5415) offers global diversified majors, digital-engineering specialists, government integrators, and managed-infrastructure operators — but no single pure-play. Payroll (a slice of accounting, 5412) is a bench of profitable, dividend-paying listed compounders (ADP, Paychex, Paycom, Paylocity). Biotech and the contract-research complex (a slice of R&D, 5417) are reachable through ETFs (XBI, IBB) and the listed CRO oligopoly (IQVIA, ICON, Medpace).

• Where listed exposure is thin, adjacent, or foreign. Advertising (5418) hides its cleanest pure-plays in a small child: billboard REITs (Lamar, OUTFRONT) and digital sell-side ad-tech; the big holding companies (Omnicom, Stagwell) span four children at once. Testing (in 5413) and environmental consulting (in 5416) have a few U.S. mid-caps and deeper foreign majors. Marketing research, translation, and veterinary (in 5419) are reached only through foreign listings, licensing platforms, or ecosystem suppliers (IDEXX, Zoetis for pets).

• Where you essentially cannot buy in at all (publicly). Legal Services (5411) — the ban on non-lawyer ownership keeps ~95% of a $375-billion industry off the exchange; the listed exposure is title insurers and legal-data vendors. Specialized Design (5414) — too fragmented to have a champion; exposure runs through design software, furniture makers, and luxury brands. The prestige cores everywhere — McKinsey, the Big Four, elite economic-consulting partnerships, non-profit research institutes — are closed to outside capital by structure.

There is no index fund for NAICS 541, and public-company revenue is never a clean read on any code — the majors span multiple children and earn much abroad. The real ownership is private, which is why Section 10 gives private routes equal weight. The through-line: for listed exposure you are effectively buying engineering, IT services, payroll, and biotech/contract research — plus a scattering of REITs, title insurers, and ecosystem suppliers — while the rest of the $2.67 trillion is a private-markets game.

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5. How the money works

Group-wide, this is a billable-hours labor business: revenue ≈ billable staff × utilization (the share of paid time billed to clients) × billing rate × realization (what is actually collected), amplified by leverage — the ratio of junior billers to senior owners. Capital intensity is low, so the returns levers are utilization, realization, revenue per professional, backlog/book-to-bill, and cash collection. Because overhead is largely fixed while a few points of utilization swing profit sharply, the whole sector carries operating leverage and generally thin-to-moderate service margins. With payroll ~42% of receipts, a hiring surge into weak bookings compresses margins fast; the constraint is talent, not money.[5][6][10]

But the economics fork wherever a child bolts a different engine onto the labor base — and those forks are the investor's cue not to treat 541 as one business:

• Labor leverage, pure — Legal, Consulting, Design, Architecture, most of Engineering: profit is billing rate × hours × realization, shared among partners.[4][5][6]
• Operating / fixed-asset leverage — Testing labs and title/settlement: heavy fixed costs (instruments, accredited labs, title plants) that throw off high incremental margins once volume covers them.[6][4]
• Float income — Payroll processors earn interest on billions of client dollars held in transit, so their profits rise with interest rates — an economics no other child shares.[5]
• Real-estate / landlord economics — Billboards inside advertising own scarce permitted locations and rent the faces; two of three U.S. majors are REITs, so funds from operations (FFO) and dividend payout — not earnings per share — are the metrics. This is the one place REIT language genuinely applies; do not force it elsewhere.[8]
• Milestones, royalties, and runway — Biotech and early-stage R&D live on long-cycle payoffs and burn cash for years; the number that matters is cash runway versus burn, not current margin.[7]
• Cash-pay medical + product — A veterinary clinic sets its own prices with no third-party payer (pet insurance covers ~4% of U.S. pets), a structural advantage human health care lacks; corporate owners monetize through the roll-up.[9]

The common thread is a fragmented, modest-margin core activity whose real value accrues to whoever adds leverage — labor, operating, float, real-estate, IP/royalty, or roll-up leverage. Our federal file carries no margin, utilization, or billing-rate series for this level, so those are drawn only from child-primer company disclosures.

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6. Demand drivers

There is no single demand cycle for 541 — a diversifying feature, and the reason to model the children separately. The demand engines run on different clocks:

• Business-cycle / discretionary: management consulting, advertising, marketing research, industrial and graphic design, and the transactional edge of legal and IT rise with confidence, deal flow, and marketing budgets — and are cut first in a downturn.[6][8][5][4]
• Construction- and capex-cyclical: architecture (the sector's leading indicator — architects are hired before ground breaks), engineering, surveying, and interior design track the building and capital cycle and are interest-rate-sensitive.[6]
• Infrastructure- and policy-stabilized: engineering, surveying, and parts of IT ride the Infrastructure Investment and Jobs Act, grid and power expansion, the AI data-center build-out, and reshoring/semiconductor plants — unusual forward visibility.[6][5]
• Regulation-mandated / defensive: testing, environmental consulting, accounting/audit and tax compliance, and language-access translation exist because a law, standard, permit, or lawsuit requires the work — the sector's most recession-resistant demand.[6][5]
• Counter-cyclical: litigation and expert-testimony consulting, restructuring advisory, and forensic work often rise when the economy sours.[6]
• Structural / secular growth: biopharma R&D outsourcing, veterinary care (pet ownership and "humanization"), and IT modernization grow largely independent of the cycle.[7][9][5]

The one force cutting across all nine children is artificial intelligence (AI). It is simultaneously a demand generator (clients pay to adopt, integrate, and govern it) and a demand destroyer (it compresses the billable hours and junior-staff leverage that generate profit) — the central structural question of the decade for every child, sharpest in commodity legal drafting, routine research, bulk translation, generic design, and first-line IT/coding, gentlest where a credentialed human is legally required (testimony, audit sign-off, a veterinarian's hands, a sealed engineering drawing). Whether AI expands each served market faster than it deflates prices is unresolved.[4][5][6][7]

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7. Regulation

The unifying feature is professional accountability with personal or firm-level licensure — but its form and strength differ so sharply across the children that regulation is itself an investment variable (a moat where it exists, a barrier to outside capital where it is strict).

• Ownership-restricting licensure (the investability wall). Legal Services is the extreme case: the American Bar Association's Model Rule 5.4 bars non-lawyers from owning a law firm, which is why no U.S. firm is public and why the investable action sits in the non-lawyer corners and vendor ecosystem.[4] Accounting is a softer version — most states require CPA firms to be majority-CPA-owned, so private equity enters through an "alternative practice structure" that splits the audit entity from the capital-taking company.[5] Veterinary has "corporate practice" rules that shape how consolidators may legally own clinics.[9]
• Individual "stamp-and-seal" licensure (a moat, not an ownership bar). Architects, professional engineers, and land surveyors sign and seal work under personal liability, state by state — reputation-based procurement (the Brooks Act) supports fees.[6]
• Accreditation rather than personal licensure. Testing labs compete on ISO/IEC 17025 accreditation; each accreditation is a competitive asset.[6]
• Regulation as the demand. Environmental consulting exists because of the statutory stack (Clean Air/Water Acts, Superfund, the PFAS drinking-water limits); translation because of civil-rights language-access mandates; testing and audit because compliance is not optional. Rule changes generally mean more billable work; simplification erodes it.[6][5]
• Light or unlicensed at entry. Consulting, design (outside interior), advertising, marketing research, and bookkeeping have essentially no licensing gate — the reason those children have the longest tails of solo operators.
• Government-contracting and cross-cutting rules. Whoever sells to Washington is bound by the Federal Acquisition Regulation, clearances, and conflict-of-interest rules; privacy law (HIPAA, GLBA, the EU's GDPR, state privacy acts), auditor-independence (Sarbanes-Oxley), and litigation-admissibility standards bind specific children; and an emerging AI-governance layer is being written into contracts across all of them.[5][6][4]

Net: one sector, a full spectrum of regulatory regimes — from an ownership wall that keeps a $375-billion child off the market to trades anyone can enter with a laptop.

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8. Consolidation

Subsector 541 is a textbook buy-and-build landscape — fragmentation near the theoretical floor (HHI 7.9), recurring demand, scarce credentialed talent, and a wave of retiring founders supplying sellers.[1] The roll-up is running in every child, but along different logics and, critically, never across children — no one is assembling scale in law firms, IT shops, and veterinary clinics at once, which is precisely why the pooled concentration is so low.

• Private equity is the shared engine. Accounting has become one of the loudest PE stories (platform deals triggering hundreds of follow-on acquisitions; a third of the largest firms now carry PE ownership); IT services is among the most active PE lanes in the economy; consulting saw over a thousand acquisitions globally in a year; veterinary, translation, testing, and the "Other" catch-all are all PE-driven roll-ups.[5][6][9]
• Strategic acquirers run in parallel. Engineering majors (WSP's multi-billion-dollar TRC and POWER deals), the testing/inspection global majors, IT strategics (Accenture's dozens of deals a year), and advertising holding companies (Omnicom's ~$13.5-billion Interpublic acquisition) buy capability constantly.[6][5][8]
• The prestige cores resist consolidation. Elite strategy partnerships, the Big Four, top economic-consulting houses, and non-profit research institutes stay independent and unbuyable because partner economics and culture — not capital — drive them.[5][6][7]

The common pattern: consolidation happens at the top and the edges of each child while the base — hundreds of thousands of small local firms — stays fragmented. The awaited catalyst in several children (notably veterinary) is a public listing of a large private platform, which would give public investors their first at-scale operator.

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9. Risks

Shared across the subsector:

• AI as the central swing variable. The same tool that creates advisory demand can deflate the billable-hours and junior-leverage model that generates profit — the defining structural risk for a labor sector, unevenly distributed across children.[4][5][6][7]
• Talent scarcity and wage inflation. The scarce, aging, credentialed workforce (engineers, CPAs, PhDs, surveyors) is both the moat and the cost pressure; the asset walks out the door.[5][6]
• Thin margins and high operating leverage. A modest revenue drop can erase profit and force layoffs of hard-to-replace staff.
• PE roll-up and leverage risk. The universal consolidation engine runs on debt; softer volumes and higher rates strain the most-levered platforms, with private-credit exposure to some roll-ups (veterinary) already under scrutiny.[9]
• Government-spending shocks. Federal cost-cutting in 2025–26 put tens of billions of consulting, research, and IT-integration fees under review and triggered terminations across the government-facing children (management, environmental, and social-science research; large IT integrators).[6][5][7]
• Measurement and mismatch risk. Employer statistics undercount the sector, and — because so many listed names are proxies or diversified parents — a public investor can own a company with the right label but little direct exposure to the code. Do not equate a public company's total revenue with a child's revenue.

Concentrated in specific children:

• Regulatory disruption of ownership (legal Rule 5.4 cracking; auditor-independence tension in PE-owned accounting) can reshape who competes.[4][5]
• Deep cyclicality in architecture, advertising, marketing research, and the transactional edges (rate- and confidence-sensitive).[6][8]
• Structural decline in the physical children (direct mail, material distribution) and commodity tiers (bulk translation, generic design/photography).[8][9]
• Fixed-price / professional-liability exposure in engineering, environmental remediation, and IT projects.[6][5]
• Funding- and cycle-dependence in biotech (clinical failure, cash burn, the "valley of death") and title/notary (mortgage-rate cyclicality).[7][4]

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10. How to invest, and the outlook

Public routes are indirect, uneven, and concentrated in a few children. For listed, liquid exposure the sector narrows to roughly four benches: engineering (diversified design/program-management firms, valued on growth-and-cyclical multiples, backlog quality, and fixed-price exposure); IT services (differentiated proxies matched to what each firm actually does, with the federal-budget overhang as a swing factor); payroll (dividend-paying compounders whose float income scales with rates); and biotech / contract research (ETFs plus the CRO oligopoly, traded on book-to-bill and pipeline, not yield). Around those sit the sector's cleaner niche pure-plays — billboard REITs (income, judged on FFO), title insurers (cyclical financials), digital ad-tech, and ecosystem suppliers to veterinary — plus diversified conglomerates (holding companies, testing/inspection majors) where the target activity is one slice. There is no index fund for the sector, so public investors make single-name bets and must strip each company down to its real exposure. The children with the biggest revenue and the ones with the best public access are, tellingly, different children.

Private routes are where most of the $2.67 trillion actually lives — and they are unusually accessible because average firm size is small. The playbook recurs across children: buy or build a practice (an accounting firm, an engineering shop, a title agency, a veterinary clinic, a design studio), back or lend to a PE roll-up platform, or take a limited-partner stake in the sponsors consolidating each fragmented base. Diligence weights what the federal stats cannot show: utilization, realization, recurring-revenue share, customer and federal-contract concentration, credential/licensure quality, owner succession, AI exposure, and — for partnerships — earnings normalized for owner compensation. The prestige cores (elite strategy, Big Four, top economic-consulting, non-profit institutes, and every U.S. law firm) remain closed to outside capital by structure.

Outlook (forward-looking judgment, not a forecast). NAICS 541 should stay large, high-wage, and economically central, but its nine children will keep diverging rather than moving as one. The durable long-run demand story — complexity, technology waves, regulation, litigation, deal activity, infrastructure, and demographic pull (pets, language access, aging drug pipelines) — is intact and has grown ahead of GDP. Against it run three tempering forces: a real near-term federal-spending shock hitting the government-facing children, deep cyclicality in the discretionary and construction-linked ones, and the unresolved AI question that could expand each served market while compressing the hours per job. The most credible value creation concentrates in two places — the engineering, IT-services, payroll, and life-science majors on the public side, and private consolidation of the fragmented base everywhere — rather than in any single pure-play. The strongest firms in every child will pair trusted human judgment with technology, proprietary tools or data, and recurring revenue; commodity, easily-automated, headcount-only work is the most exposed to price pressure. This is an industry framework, not a recommendation of any security. For the complete company tables, unit economics, and diligence checklists, read the nine child primers (5411–5419).

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Sources

Headline figures for this level ([1] receipts/firms/concentration; [2] establishments/employment/payroll) are our ingested ground-truth federal statistics for NAICS 541 (stats-541.md). Child-level shares, ownership detail, and named companies are drawn from the nine child primers, whose own numbered sources give the underlying filings and releases.

1. U.S. Census Bureau, 2022 Economic Census — Concentration of Largest Firms, NAICS 541 (receipts $2,667,262,040 thousand; 876,176 firms; CR4 3.8% / CR8 6.3% / CR20 10.4% / CR50 16.3%; HHI 7.9). Histometrics ingested federal statistics. https://data.census.gov/table/ECNSIZE2022.EC2200SIZECONCEN
2. U.S. Census Bureau, County Business Patterns 2023 — NAICS 541 (989,182 establishments; 10,401,442 employees; $1,114.42B annual payroll; $279.77B Q1 payroll; employer-only coverage). Histometrics ingested federal statistics. https://www.census.gov/programs-surveys/cbp.html
3. U.S. Census Bureau, 2022 NAICS Structure — Sector 54 / Subsector 541, Professional, Scientific, and Technical Services, and its industry groups 5411–5419 (definitions and hierarchy). https://www.census.gov/naics/?year=2022
4. Histometrics rollup primer, NAICS 5411 Legal Services ($374.6B receipts; HHI 10.3; Rule 5.4 non-lawyer-ownership ban; title insurers, legal-data/AI vendors, litigation finance). primer-5411-DRAFT.md.
5. Histometrics rollup primer, NAICS 5412 Accounting, Tax Preparation, Bookkeeping, and Payroll Services ($208.9B receipts; HHI 300.4; Big Four; PE roll-up; payroll and tax public plays). primer-5412-DRAFT.md.
6. Histometrics rollup primer, NAICS 5413 Architectural, Engineering, and Related Services ($406.5B receipts; HHI 19.9; engineering + testing public bench; licensure, IIJA, PFAS). primer-5413-DRAFT.md.
7. Histometrics rollup primer, NAICS 5417 Scientific Research and Development Services ($340.5B receipts; HHI 59; biotech ETFs, CRO complex, federal contractors, non-profit institutes; BIOSECURE Act). primer-5417-DRAFT.md.
8. Histometrics rollup primer, NAICS 5418 Advertising, Public Relations, and Related Services ($134.8B receipts; HHI 79.3; holding companies, billboard REITs, digital ad-tech; Omnicom–Interpublic). primer-5418-DRAFT.md.
9. Histometrics rollup primer, NAICS 5419 Other Professional, Scientific, and Technical Services ($129.6B receipts; HHI 54.8; veterinary anchor, Mars/JAB/PE; ecosystem stocks IDEXX/Zoetis; no listed pure-play). primer-5419-DRAFT.md.
10. Histometrics rollup primer, NAICS 5415 Computer Systems Design and Related Services ($600.6B receipts; HHI 49.9; global majors, digital-engineering specialists, gov integrators; PE roll-up). primer-5415-DRAFT.md.
11. Histometrics rollup primer, NAICS 5416 Management, Scientific, and Technical Consulting Services ($435.0B receipts; HHI 43.6; McKinsey/BCG/Bain/Big Four private; Exponent/CRA/Montrose proxies). primer-5416-DRAFT.md.
12. Histometrics rollup primer, NAICS 5414 Specialized Design Services ($36.8B receipts; HHI 4.8; interior/industrial/graphic; no listed pure-play; design software, furniture, luxury proxies). primer-5414-DRAFT.md.
13. U.S. Department of Justice, Herfindahl-Hirschman Index (markets below ~1,500 generally unconcentrated under DOJ/FTC guidelines), 2023. https://www.justice.gov/atr/herfindahl-hirschman-index