EMPLOYMENT AND UNEMPLOYMENT

U.S. BUREAU OF LABOR STATISTICS

FEBRUARY 2014 • VOLUME 3/ NUMBER 3 

U.S. BUREAU OF LABOR STATISTICS | FEBRUARY 2014 1 www.bls.gov

Measuring occupational concentration by industry

Author: Audrey Watson

Although some occupations are found in nearly every 

industry in the United States, others are specific to 

one or only a few industries. For example, several of 

the most concentrated occupations in the coal mining industry 

are found primarily in that industry, and are uncommon outside 

of the mining and extraction sector. As a result, job mobility for 

these workers might be extremely limited in the face of an industry 

downturn, particularly one affecting the extraction industries in 

general. On the other hand, although over a quarter of computer 

systems analysts are found in the computer systems design 

and related services industry, this occupation was distributed 

relatively evenly across sectors, potentially allowing displaced 

workers to move more easily into other industries. Understanding 

the relationship between industry and occupation may provide 

important insights into workers’ ability to cope with job loss by 

moving across industries. 

Related articles

More BLS articles and information related to 

occupational employment are available online at 

the following links: 

y “Using Location Quotients to Analyze 

Occupational Data” www.bls.gov/oes/

highlight_location_quotients.pdf.

y “Mapping out a career: An analysis of 

geographic concentration of occupations” 

www.bls.gov/opub/ooq/2010/

fall/art02.htm.

y “Science, technology, engineering, and 

mathematics (STEM) occupations: A visual 

essay” www.bls.gov/opub/mlr/

2011/05/art1full.pdf.
U.S. BUREAU OF LABOR STATISTICS | FEBRUARY 2014 2 www.bls.gov

BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

This BEYOND THE NUMBERS article uses two tools—

the Herfindahl-Hirschman index (HHI) and industry 

quotients—to measure occupational specialization 

by industry. Although some industries use specialized 

labor highly intensively, others rely on less specialized 

occupations that are also prevalent elsewhere in the 

economy. These differences in industry staffing patterns 

may affect workers’ ability to respond effectively and 

flexibly to changes in the economy. Occupations 

concentrated in a single industry, such as travel agents 

or shoe machine operators and tenders, may require 

skills that are highly specific to that industry. If workers 

in these occupations become unemployed, it may be 

difficult for them to use their skills in other industries. 

However, workers in more widely distributed occupations 

may find it easier to transfer their skills in response to job 

loss. Occupational composition also may affect a growing 

industry’s ability to attract workers from elsewhere in the 

economy. For example, industries that rely on specialized, 

highly qualified workers may find that the high skill and 

training requirements act as a barrier to entry for displaced 

workers from other sectors. 

Several different measures are available for examining 

the industry and occupation relationship. Traditional 

tools include measuring the share of total occupational 

employment found in a given industry, as well as the 

share of total industry employment made up of a specific 

occupation. For instance, 62 percent of registered nurses 

were employed in hospitals in May 2012, and registered 

nurses made up 29 percent of total hospital employment, 

showing a strong relationship between this industry and 

occupation. 

However, these statistics provide only a partial picture of 

the relationship between occupation and industry. For 

example, they don’t offer a convenient way of comparing 

which occupations are most and least concentrated 

by industry, nor do they allow for easy identification 

of industries that use specific occupations intensively. 

The HHI and industry quotients are additional tools that 

provide a complementary perspective on the industry and 

occupation relationship. 

Herfindahl-Hirschman indexes for 

occupational groups

The HHI is normally used to measure market concentration 

among firms in an industry; here, it is used to provide 

an overall measure of occupational concentration by 

industry. In general, a higher HHI indicates that the 

occupation or occupational group was found primarily in 

a few industries, whereas a lower value indicates that the 

occupation or occupational group was spread more evenly 

across industries. An occupation or occupational group 

found entirely in a single industry will have an HHI with the 

maximum possible value of 10,000.1

The concentration of occupational groups across industry 

sectors, based on an aggregated HHI, is shown in chart 

1. The aggregated HHI for each occupational group is a 

weighted average of the HHIs for the individual detailed 

occupations in that group, with each occupation’s 

HHI weighted by the occupation’s share of total group 

employment. Thus, occupations with high employment 

levels have more influence than occupations with low 

employment levels on the aggregate HHI, allowing the 

aggregate index to reflect more closely the industry 

concentration patterns of the occupations that make up 

the majority of jobs in the group. In some cases, weighting 

had a substantial effect on the aggregate HHI. For example, 

if the HHI for the transportation and material moving 

group is constructed by taking a simple average of the 

indexes of its detailed occupations, the result is nearly 74 

percent higher than the weighted average HHI shown 

in chart 1. This reflects, in part, the fact that the largest 

occupation in this group—laborers and hand freight, 

stock, and material movers—made up nearly a quarter of 

the occupational group employment and had one of the 

lowest industry concentrations of any transportation and 

material moving occupation. The aggregated HHIs also 

differ from HHIs constructed directly from the major group 

employment data in that the latter capture only the overall 

distribution of each group across industries, whereas 

averaging the occupation-specific HHIs incorporates the 

industry distribution of the detailed occupations within 

each group.2
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

The most widely dispersed occupational groups included 

computer and mathematical, management, office and 

administrative support, and business and financial 

operations occupations. These groups tend to contain 

jobs that are in demand in many types of businesses. For 

example, office and administrative support occupations 

such as executive secretaries and executive administrative 

assistants, customer service representatives, and general 

office clerks provide support functions applicable to a 

wide range of industries. Similar support occupations 

in the business and financial operations group include 

accountants and auditors; purchasing agents; and 

meeting, convention, and event planners. 

Although the management group includes some highly 

specialized occupations, such as funeral service managers 

or lodging managers, other management occupations 

involve overseeing functional areas relevant to many 

industries, such as sales, marketing, purchasing, and 

finance. Nearly all of the computer and mathematical 

occupations were widely distributed across industry 

sectors. Except for actuaries, all of the occupations in this 

group had individual HHIs below 3,000, compared with 

only about one-quarter of occupations overall. Computer 

and mathematical occupations with the lowest industry 

concentrations included network and computer systems 

administrators, computer user support specialists, and 

database administrators.

Several of the most concentrated occupational groups 

had specialized job duties that were directly related to 

the primary activities of the industries in which they were 

concentrated. For example, 89 percent of education, 

training, and library jobs were in the educational services 

Chart 1

0 2,000 4,000 6,000 8,000 10,000

Education, training, and library

Healthcare support

Healthcare practitioners and technical

Food preparation and serving related

Protective service

Sales and related

Construction and extraction

Production

Community and social service

Personal care and service

Farming, fishing, and forestry

Legal

Arts, design, entertainment, sports, and media

Architecture and engineering

Life, physical, and social science

Building and grounds cleaning and maintenance

Transportation and material moving

Installation, maintenance, and repair

Business and financial operations

Office and administrative support

Management

Computer and mathematical

Herfindahl-Hirschman index

Occupational groups by industry concentration, May 2012 

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Note: These measures represent a weighted average Herfindahl-Hirschman index by occupational group, calculated by NAICS sector. The 

higher the number, the more an occupational group is concentrated in fewer industry sectors.
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

sector, and 88 percent of healthcare support jobs were in 

the health care and social assistance sector.3 Eighty-one 

percent of employment in food preparation and serving 

related occupations was in the accommodation and food 

services sector.

Herfindahl-Hirschman indexes for 

detailed occupations

Although some occupational major groups were, on 

average, more concentrated than others, individual 

detailed occupations within a given group could vary 

greatly in their degrees of industry concentration. For 

example, the installation, maintenance, and repair group 

had an aggregated HHI of about 2,800, but HHIs for 

individual occupations within this group ranged from 

855 for first-line supervisors of mechanics, installers, and 

repairers to 9,222 for bicycle repairers. 

Detailed occupations that were spread most evenly across 

industry sectors, as measured by low HHIs, are shown in 

chart 2. These included two management occupations 

with broad job duties: chief executives and general and 

operations managers. Most of the remaining occupations 

shown were related to human resources or general office 

administration. Human resources occupations with low 

industry concentrations ranged from the managerial 

level through the clerical level, and included human 

resources managers; training and development managers; 

training and development specialists; human resources 

assistants, except payroll and timekeeping; and payroll 

and timekeeping clerks. Occupations associated with 

general office administration included administrative 

services managers; first-line supervisors of office and 

administrative support workers; computer operators; 

secretaries and administrative assistants, except legal, 

Chart 2

0 200 400 600 800 1,000

General and operations managers

Bookkeeping, accounting, and auditing clerks

Chief executives

Office clerks, general

Payroll and timekeeping clerks

First-line supervisors of mechanics, installers, and repairers

Training and development specialists

Administrative services managers

Secretaries and administrative assistants, except legal, medical, and ...

Executive secretaries and executive administrative assistants

First-line supervisors of office and administrative support workers

Computer operators

Training and development managers

Human resources managers

Human resources assistants, except payroll and timekeeping

Herfindahl-Hirschman index

Occupations with the lowest industry concentrations, May 2012

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Note: Industry concentration is measured by the Herfindahl-Hirschman index, calculated by NAICS sector.

Secretaries and administrative assistants, except legal, medical, and executive
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

medical, and executive; executive secretaries and 

executive administrative assistants; general office clerks; 

and bookkeeping, accounting, and auditing clerks. Overall, 

these occupations may allow for more mobility among 

jobseekers as they look for jobs in various industries.

Detailed occupations with perfect or near-perfect 

concentration in a single industry sector, as indicated 

by HHIs of approximately 10,000, included a number of 

occupations specific to government, such as postmasters 

and mail superintendents, postal service mail carriers, and 

other postal service occupations; legislators; tax examiners 

and collectors, and revenue agents; judges, magistrate 

judges, and magistrates; and fish and game wardens. 

Postsecondary teaching occupations made up most of 

the remaining occupations with HHIs of about 10,000, 

reflecting their high concentration in the educational 

services sector. Such occupations may limit jobseekers to 

specific industries. 

Aside from postsecondary teaching occupations and 

government-specific occupations, occupations with nearperfect industry concentration included mine shuttle 

car operators, mining roof bolters, orthodontists, funeral 

attendants, chiropractors, and shampooers. Many of 

these occupations were concentrated not only in a single 

industry sector, but in a specific detailed industry within 

that sector. For example, nearly all funeral attendants were 

employed in the death care services industry, part of the 

other services (except federal, state, and local government) 

sector. 

HHIs for the occupations with the highest employment in 

May 2012 are shown in chart 3. Total employment in these 

occupations ranged from about 2.1 million for secretaries 

and administrative assistants, except legal, medical, and 

executive, to over 4.3 million for retail salespersons. 

In terms of their industry concentrations, the occupations 

in chart 3 fall into two broad categories: half had HHIs of 

less than 2,500, while the remainder had much higher 

HHIs of approximately 7,000 to 9,000. Occupations in the 

first category tended to be spread across multiple industry 

sectors, where they were found in numbers sufficient to 

Chart 3

0 2,500 5,000 7,500 10,000

Retail salespersons

Cashiers

Combined food preparation and serving workers, including fast food

Office clerks, general

Registered nurses

Waiters and waitresses

Customer service representatives

Laborers and freight, stock, and material movers, hand

Janitors and cleaners, except maids and housekeeping cleaners

Secretaries and administrative assistants, except legal, medical, and ...

Herfindahl-Hirschman index

Occupations with the highest employment, by industry concentration, May 2012

Note: Industry concentration is measured by the Herfindahl-Hirschman index, calculated by NAICS sector.

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Secretaries and administrative assistants, except legal, medical, and executive
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

produce high overall employment levels. Occupations in 

this category were general office clerks; customer service 

representatives; laborers and freight, stock, and material 

movers, hand; janitors and cleaners, except maids and 

housekeeping cleaners; and secretaries and administrative 

assistants, except legal, medical and executive.

However, occupations found primarily in a single sector 

also could have very high employment levels, provided 

they made up a sufficiently large share of employment in 

the sectors in which they were concentrated. For example, 

registered nurses was the largest occupation in the largest 

industry sector, health care and social assistance. Eightyseven percent of registered nurses were employed in 

this sector, where they made up about 1 out of every 8 

jobs. Similarly, retail salespersons and cashiers combined 

made up about 45 percent of employment in the secondlargest industry sector, retail trade, although fewer than 20 

percent of cashiers and 10 percent of retail salespersons 

were employed outside of the retail trade sector.

HHIs for a very different group of selected occupations—

science, technology, engineering, and mathematics (STEM) 

occupations—are shown in chart 4. Unlike the largest 

occupations from chart 3, STEM occupations tended to be 

high paying: with the exception of forest and conservation 

technicians, all of the occupations in chart 4 had annual 

mean wages above the U.S. average of $45,790, while all 

of the largest U.S. occupations except registered nurses 

had below-average wages. However, like the largest U.S. 

occupations, STEM occupations varied greatly in their 

degrees of industry concentration. 

Many of the most widely distributed STEM occupations 

were computer occupations, reflecting the importance 

of information technology to a variety of industries. Of 

0 2,500 5,000 7,500 10,000

Forest and conservation technicians

Forensic science technicians

Industrial engineering technicians

Conservation scientists

Architectural and civil drafters

Computer and information systems managers

Computer network support specialists

Database administrators

Computer user support specialists

Network and computer systems administrators

Herfindahl-Hirschman index

Science, technology, engineering, and mathematics (STEM) occupations with the highest and lowest 

industry concentrations, May 2012

Note: Industry concentration is measured by the Herfindahl-Hirschman index, calculated by NAICS sector. Light bars indicate STEM 

occupations with the lowest Herfindahl-Hirschman indexes. STEM occupations are defined here to include life and physical science, 

engineering, mathematics, and computer occupations, along with the corresponding management occupations.

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Chart 4
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

the five STEM occupations with HHIs below 1,500, all were 

computer related: computer and information systems 

managers, computer network support specialists, database 

administrators, computer user support specialists, and 

network and computer systems administrators. Other 

computer occupations with low industry concentrations 

included computer systems analysts, web developers, and 

computer network architects (not shown in the chart). 

Outside of the computer group, STEM occupations with 

low industry concentrations included health and safety 

engineers, except mining safety engineers; electronics 

engineers, except computer; and electrical and electronics 

engineering technicians.

STEM occupations with the highest industry concentrations 

included forest and conservation technicians, forensic science 

technicians, industrial engineering technicians, conservation 

scientists, and architectural and civil drafters, all with HHIs 

of 6,000 or higher. Three of these occupations were found 

mainly in government. Ninety-six percent of forest and 

conservation technicians and 93 percent of forensic science 

technicians were employed in the public sector, with forest 

and conservation technicians found primarily in federal 

government and forensic science technicians found primarily 

in local government. Eighty-one percent of conservation 

scientists were employed in the public sector; nearly half of 

these jobs were in federal government, with the remainder 

split between state and local government. Seventy-nine 

percent of architectural and civil drafters were found in the 

professional, scientific, and technical services sector, primarily 

in the architectural, engineering, and related services industry. 

Seventy percent of industrial engineers were employed 

in manufacturing. Although no single manufacturing 

industry accounted for the majority of industrial engineers, 

manufacturing industries with the highest employment 

of this occupation included aerospace product and parts 

manufacturing; motor vehicle parts manufacturing; and 

navigational, measuring, electromedical, and control 

instruments manufacturing.

Industry quotients overview 

The HHI provides a useful summary statistic for measuring 

an occupation’s overall degree of industry concentration, 

but does not show the specific industries in which 

an occupation is used intensively. An alternative is to 

examine occupational concentrations using a variation 

of location quotients, a tool more commonly used to 

analyze data by geographic area. As used with respect 

to occupational employment data, the standard location 

quotient represents the ratio of an occupation’s share of 

area employment to its share of national employment. The 

variation used here, called an “industry quotient” for the 

purpose of this Beyond the Numbers article, represents the 

ratio of the occupation’s share of employment in a specific 

industry to its share of employment in all industries 

combined. An industry quotient greater than one indicates 

that the occupation makes up a greater share of industry 

employment than it does of overall employment. For 

example, an occupation that makes up 10 percent of 

employment in a given industry but only 2 percent of total 

employment would have an industry quotient of 5 for that 

industry, indicating the industry’s relative reliance on this 

type of labor is 5 times the average. 

In geographic area analysis, high location quotients 

do not necessarily imply high employment levels of an 

occupation. Very large metropolitan areas, for example, 

tend to have high employment of most individual 

occupations, even if those occupations have lower shares 

of area employment relative to the national average. A 

similar caveat applies to industry quotients: a high industry 

quotient for an occupation indicates that the industry 

uses that occupation more intensively than average, 

but depending on the overall size of the industry, it may 

or may not have high absolute employment levels for 

that occupation. For example, the household appliance 

manufacturing industry had an industry quotient of 35 

for team assemblers, but had employment of only about 

15,000 in this occupation. By comparison, the much larger 

employment services industry had about 177,000 team 

assembler jobs, but had a much lower—although still 

above average—industry quotient of 7 for the occupation. 

For this reason, it is helpful to look at industry quotients in 

conjunction with other data, such as the actual number of 

jobs and the percentage of total occupational employment 

found in the industry.
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0 1 2 3 4 5 6 7 8 9 10

Accounting, tax preparation, bookkeeping, and payroll services

Office administrative services

Offices of real estate agents and brokers

Petroleum and petroleum products merchant wholesalers

Land subdivision

Freight transportation arrangement

Farm product raw material merchant wholesalers

Lessors of nonfinancial intangible assets (except copyrighted 

works)

Activities related to real estate

Management of companies and enterprises

Industry quotient

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Industries with the highest industry quotients for bookkeeping, accounting, and auditing clerks, 

May 2012

BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

Industry quotients varied considerably by occupation. 

For some widespread occupations, industry quotients 

were relatively low even in the industries in which these 

occupations were used most intensively. Chart 5 shows 

the industries with the highest industry quotients for 

bookkeeping, accounting, and auditing clerks, one 

of the occupations with the lowest overall industry 

concentrations as shown in chart 2. Bookkeeping clerks 

had industry quotients of 9 in the accounting, tax 

preparation, bookkeeping, and payroll services industry 

and 5 in the office administrative services industry. In 

both of these industries, the primary business activities 

were directly related to the job duties of this occupation. 

Bookkeeping clerks had an industry quotient of less than 4 

in every other industry. 

The highest industry quotients for other widespread 

occupations were similarly moderate. For example, the 

highest industry quotient for first-line supervisors of 

mechanics, installers, and repairers was about 14 (in the 

automotive repair and maintenance industry), and the 

highest industry quotient for human resources specialists 

was approximately 7 (in the employment services 

industry).

Where some of the highest industry quotients for some 

occupations were relatively low, industry quotients for 

other occupations ranged into the hundreds or even 

thousands. For example, shoe machine operators and 

tenders had an industry quotient of over 9,000 in the 

footwear manufacturing industry, and both fallers and 

logging equipment operators had industry quotients 

of over 2,000 in the logging industry. These industry 

quotients are extremely high because these occupations 

were highly concentrated in relatively small industries, but 

had low overall employment levels—in other words, the 

industry quotients had both high numerators and very low 

denominators. For example, shoe machine operators and 

tenders made up about 24 percent of employment in the 

small U.S. footwear manufacturing industry, but with total 

Chart 5
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

employment of about 3,400, this occupation represented 

less than .003 percent of total national employment.

Industry quotients—an industry 

perspective

Looking at industry quotients from the industry 

perspective reveals that some industries had several 

occupations with extremely high industry quotients, 

while in other industries, even the occupations with the 

highest industry quotients had only moderately high 

concentrations relative to the national average. These 

patterns suggest that industries vary considerably in their 

use of specialized, industry-specific labor. 

The office administrative services industry is an example 

of an industry with a relatively low degree of occupational 

specialization. Even for the occupations used most 

intensively in this industry, industry quotients were 

moderate, ranging from nearly six for mail clerks and mail 

machine operators, except postal service to nine for both 

bill and account collectors and billing and posting clerks. 

(See chart 6.) 

Although the occupations shown in chart 6 had aboveaverage concentrations in the office administrative 

services industry, they made up only about 10 percent of 

total industry employment combined, and most jobs in 

these occupations were found in other industries. Of the 

occupations in chart 6, only billing and posting clerks, 

with industry employment of 13,650, and bill and account 

collectors (10,720) were among the largest occupations 

in the office administrative services industry. Credit 

counselors, training and development managers, and 

private detectives and investigators each had industry 

employment of less than 1,000. By comparison, customer 

service representatives, the largest occupation in the office 

administrative services industry, had industry employment 

of over 34,000. In addition, the office administrative 

services industry accounted for less than 3 percent of total 

employment in each of the occupations in chart 6.

The occupations with the highest industry quotients in the 

computer systems design and related services industry 

are shown in chart 7. The majority of these occupations 

were from the computer and mathematical occupational 

group. The only occupation from outside of this group, 

Chart 6

0 2 4 6 8 10

Billing and posting clerks

Bill and account collectors

Credit counselors

Office and administrative support workers, all other

Data entry keyers

Training and development managers

Private detectives and investigators

Computer operators

Medical records and health information technicians

Mail clerks and mail machine operators, except postal service

Industry quotient

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Occupations with the highest industry quotients in the office administrative services industry, May 2012
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

computer hardware engineers, also had job duties directly 

related to information technology. Although still moderate 

compared with those in many other industries, the highest 

industry quotients in computer systems design and related 

services were higher than those in office administrative 

services, ranging from about 17 for computer network 

support specialists, computer hardware engineers, and 

web developers to 32 for computer programmers. 

Compared with office administrative services, the 

computer systems design and related services industry 

employed a more substantial share of the occupations 

used intensively in the industry, and these occupations 

made up a higher percentage of total industry 

employment. The occupations in chart 7 combined made 

up 45 percent of total employment in computer systems 

design and related services. Four of the occupations 

with the highest industry quotients also were the four 

largest occupations in the industry: applications software 

developers, with industry employment of 199,080; 

computer systems analysts (136,910); systems software 

developers (125,250); and computer programmers 

(122,790). In addition, the computer systems design 

and related services industry accounted for more than 

one-fifth of total occupational employment in each of 

the occupations shown in chart 7, rising to 34 percent 

for applications software developers and 39 percent for 

computer programmers. 

However, the occupations shown in chart 7 were still 

widely found outside of computer systems design. For 

example, occupations like web developers, computer 

systems analysts, and computer network architects were 

associated with IT support functions in many industries, 

while computer network support specialists was among 

the STEM occupations most widely distributed across 

industries, as shown in chart 4. 

0 5 10 15 20 25 30 35

Computer programmers

Software developers, applications

Software developers, systems software

Computer systems analysts

Computer network architects

Information security analysts

Mathematical science occupations, all other

Web developers

Computer hardware engineers

Computer network support specialists

Industry quotient

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Occupations with the highest industry quotients in the computer systems design and related services 

industry, May 2012

Chart 7
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

In contrast to the industries featured in charts 6 and 

7, coal mining is an example of an industry containing 

occupations that were both very intensively used and 

highly industry specific, as shown in chart 8. All of the most 

intensively used occupations in the coal mining industry 

had job duties directly related to the mining process, and 

most had limited employment outside of the extraction 

sector. Three occupations had industry quotients of over 

1,000 in the coal mining industry, and a fourth occupation 

had an industry quotient of nearly 800. Two of these four 

occupations—mine shuttle car operators and mining 

roof bolters—were nearly exclusive to the coal mining 

industry, which contained 96 percent of employment in 

each occupation. Underground mining loading machine 

operators and continuous mining machine operators also 

were found primarily in coal mining, which accounted for 

71 percent and 54 percent, respectively, of employment in 

these two occupations. 

The remaining occupations in chart 8 had industry 

quotients ranging from 145 for excavating and loading 

machine and dragline operators to 575 for mine cutting 

and channeling machine operators. Of the occupations 

in chart 8, only mining and geological engineers and 

excavating and loading machine and dragline operators 

had significant employment outside of the mining sector. 

Thirty percent of mining and geological engineers worked 

in the architectural, engineering, and related services 

industry, compared with 44 percent in coal mining and 

other mining and extraction industries. About 43 percent 

of excavating and loading machine and dragline operators 

were employed in the construction sector, compared with 

about 31 percent in mining and extraction industries. 

Eighty-five percent or more of employment in the 

0 500 1,000 1,500 2,000

Mine shuttle car operators

Roof bolters, mining

Loading machine operators, underground mining

Continuous mining machine operators

Mine cutting and channeling machine operators

Mining machine operators, all other

Extraction workers, all other

Helpers—extraction workers

Mining and geological engineers, including mining 

safety engineers

Excavating and loading machine and dragline operators

Industry quotient

Occupations with the highest industry quotients in the coal mining industry, May 2012

Source: U.S. Bureau of Labor Statistics, special tabulation of May 2012 Occupational Employment Statistics data.

Chart 8
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BEYOND THENUMBERS EMPLOYMENT AND UNEMPLOYMENT

Notes

1. The standard version of the Herfindahl-Hirschman index is calculated by squaring each firm’s market share and then summing 

the results. For example, a market containing five firms with shares of 10, 15, 20, 25, and 30 percent would have an HHI of 

(10)2 + (15)2 + (20)2 + (25)2 + (30)2 = 100 + 225 + 400 + 625 + 900 = 2,250. For the purpose of this Beyond the Numbers article, 

market shares were replaced in the calculation by the shares of the occupation’s total employment found in each industry. 

An occupation with 100 percent of its employment in a single industry would have an HHI of (100)2 = 10,000. HerfindahlHirschman indexes presented in this section were calculated based on 2010 Standard Occupational Classification (SOC) 

detailed occupations and 2012 North American Industry Classification System (NAICS) 2-digit sectors and supersectors.

Industry. A group of business establishments that produce similar products or provide similar services. For 

example, all establishments that manufacture automobiles are in the same industry. A given industry, or 

even a particular establishment in that industry, might have employees in dozens of occupations. Industry 

classification in the May 2012 OES data is based on the 2012 North American Industry Classification System 

(NAICS).

Occupation. A set of activities or tasks that employees are paid to perform. Employees that perform essentially 

the same tasks are in the same occupation, whether or not they work in the same industry. Some occupations 

are concentrated in a few particular industries; other occupations are found in many industries. The May 2012 

OES data use the 2010 Standard Occupational Classification (SOC) system to classify jobs into occupations.

Glossary

remaining four occupations—mine cutting and channeling 

machine operators, all other mining machine operators, all 

other extraction workers, and extraction worker helpers—

was found in coal mining or other mining and extraction 

industries. 

Although identifying the industries with the highest 

employment of each occupation is a good first step, the 

HHI and industry quotients offer additional perspectives 

on industry staffing patterns, helping to provide a more 

accurate picture of the distribution of occupations across 

industries. Such information could be useful for workers as 

they choose a career, jobseekers as they narrow or broaden 

their job searches, and employers as they try to recruit 

workers from other industries, based on the HHI and 

industry quotient for a particular occupation. 

This BEYOND THE NUMBERS article was prepared by 

Audrey Watson, economist, in the office of Occupational 

Employment Statistics. Complete OES data, including 

data highlighted in this report, are available from the OES 

website at www.bls.gov/oes/. Email: OESinfo@bls.gov; 

Telephone: (202) 691-6569. 

Information in this article will be made available to 

sensory-impaired individuals upon request. Voice phone: 

(202) 691-5200. Federal Relay Service: 1-800-877-8339. 

This article is in the public domain and may be reproduced 

without permission.

Suggested citation

Audrey Watson, “Measuring Occupational 

Concentration by Industry,” Beyond the Numbers: 

Employment and Unemployment, vol. 3, no. 3 

(Bureau of Labor Statistics, February 2014). 

http://www.bls.gov/opub.btn/volume-3/measuringoccupational-concentration-by-industry.htm.

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2. For example, consider an occupational major group consisting of four detailed occupations, each with employment of 100, 

distributed among four industries. At one extreme, the occupations could be distributed so that each industry contains all of 

the employment in one of the occupations; alternatively, each industry could contain 25 jobs in each of the four occupations. 

In the first scenario, because each occupation is perfectly concentrated in a single industry, each of the individual occupations 

has a Herfindahl-Hirschman index of 10,000; taking an average of the individual HHIs (either weighted or unweighted, in this 

example) produces an average HHI for the major group of 10,000. In the second case, each industry contains 25 percent of 

each occupation, so each of the individual occupations has an HHI of (25)2 + (25)2 + (25)2 + (25)2 = 2,500, and the (weighted or 

unweighted) average HHI for the group is also 2,500. However, in both cases, employment in each industry is 100, or 25 percent 

of total major group employment, and constructing the HHI directly from the major group data will result in an index of 2,500 

for the major group, regardless of the very different distributions of the individual detailed occupations in the two scenarios.

3. OES data for the educational services sector include private, state, and local government schools; data for the health care and 

social assistance sector include private sector establishments and state and local government hospitals.