1. science
2. mathematics
3. statistics

The how and why of statistical
classifications1
! Michel Boeda*
Statisticians rely on coordinated classifications to map the economic and social sphere. They use regulatory
classifications—chiefly because they are required to do so—and statistical classifications, which they create or help
to develop. Moreover, the European Union framework is a driver for close harmonization of national classifications.
Their convergence, now largely complete in the area of economic production, is still in progress in the socio-economic
field.
S
inevitably a complicated, imperfect,
and problematic process that requires
complex solutions (see article by Pinel).
There is no exact correspondence
between one or more items of the old
and new classifications; otherwise,
the “revision” would simply involve
switching categories (why bother?) or
nesting (change of scale).
tatisticians measure entities that
have been defined beforehand
in a field that has been identified,
named, bounded, and “cadastered”—
one might say “taxonomized.” They
can use the most refined level of a
classification like a zoom, a detailed
level beyond which the possibility
or significance of the measurement
is lost. From another angle, the
aggregated (“collapsed”) levels offer
summary information.
Classifications age because reality
changes. Classifications need to
be revised periodically, but that is a
difficult exercise for statisticians. The
linkage between consecutive series is
* Michel Boeda was Head of the Classifications
Division at INSEE’s Head Office, 1989-1995, then
Deputy Head of the Statistical and Accounting
Standards Department, and has ended his
career at CEFIL (INSEE’s Training Center in
Libourne), where, among other projects, he
organized seminars to prepare statisticians from
the European Union accession countries for
their new statistical environment.
1. Originally published as “Les nomenclatures
statistiques: pourquoi et comment,” Courrier
des statistiques (French series), no. 125, Nov.Dec. 2008, pp. 5-11, http://www.insee.fr/fr/ffc/
docs_ffc/cs125b.pdf.
Overview of classifications
Source: Wikipedia
Statisticians
(here:
official
statisticians) are involved in many
fields but use only a limited number
of coordinated classifications. We
can link classifications—for example,
those of activities and products
(which are symmetrical) and those
of occupations and social categories
(which are nested). We can also
combine them (specializations and
educational attainment) or create
networks.
Nesting is precisely the key to
international comparability, and
especially to European Union (EU)
harmonization, now essential.
Systema Naturæ (“The Systems of Nature”)
(1748), by the taxonomist Carl Von Linnæus
Statisticians begin by finding their
bearings in a territory and laying
down markers in areas that have
largely been classified without their
participation, such as accounting,
law, and regulations.
Box 1: Nomenclatures and classifications
In ancient Rome, the nomenclator was the usher who announced the names
and titles of senators—a Nomenklatura before its time! The term “nomenclature”
refers to the concept of naming. “Classifications” are more suggestive of the
need to organize knowledge categories.
The structuring of the economic and social sphere has been a very gradual process.
International harmonization is recent and incomplete. Some typologies are built
from data analyses and intended mainly for study purposes. Multiple-use statistical
classifications are informed by principles and objectives. To identify—for example,
in a business register or by assigning a geographic code—is not to classify.
The terms “nomenclature” and “classification” exist in French and English. French
speakers tend to use the first, English speakers the second. We can treat them as
synonyms, each focusing on one aspect of the concept: a system for filing items
in drawers, with specific instructions on what goes where (classification), and a
set of labels describing the general content of each drawer (nomenclature).
Courrier des statistiques, English series no. 15, 2009
3
Michel Boeda
Box 2: Classifications and mathematics
Partition
A “flat” (single-level) classification forms
a partition of the field studied that is
a breakdown into disjoint equivalence
classes. A multi-level classification
consists of nested partitions.
Partitions have a “lattice structure”
with respect to nesting, just as whole
numbers do with respect to divisibility:
A nests within B, B nests within A, or
there is no nesting. Like least common
multiples (LCMs) and largest common
denominators (LCDs), the “product”
classification (intersection of two
classifications) is the one in which we
need to collect information if we want
to publish results in both classifications;
the “sum” classification (union) is the
one in which we can compare the
result of the data collected in either
classification (Arkhipoff, 1976).
We can identify equivalence classes
(codes, descriptions) but there
is no natural order. An international
classification cannot serve as a bank of
basic items and, at the same time, supply
But statisticians also contribute to
the evolution of regulatory, economic,
social, and other standards. One
example is national accounting,
which defines and organizes flows
in the economic system. Similarly,
sociodemographic statistics explore
different aspects of people and their
relationship to work, an indicator of
social category. Statisticians flesh
out and arrange the administrative
foundations, thereby helping to
structure the economic and social
sphere.
French administrative territorial
units, from regions to municipalities
(communes), are the fruit of our
history: regions are ranked in NUTS
(EU Nomenclature of Territorial Units
for Statistics) at the second level,
the 36,000 communes at the fifth
level. These indivisible atoms of the
French Geographic Code account for
about one-third of EU items—hardly
a balanced situation. There are a
host of other geographic divisions
that statistical methods have helped
to define. Special mention should
be made of “employment areas”
(zones d’emploi), which are based
4
the nested aggregation categories for
national classifications.
Tree structure
Classifications (espalier tree structures)
fall within the scope of graph theory.
This approach is better suited to
research on the “closeness” of two
classifications,
notably
between
countries, by specifying a “distance”
between tree structures. We can also
assess the homogeneity of “more or
less dense” tree structures using an
entropic concept (disaggregation vs.
aggregation) applied to information
distribution.
INSEE has taken part in a European
research project implicitly aimed at
transcending dialectical debates by
means of a technical approach, notably
for revising the international product
classification. There are indeed three
ways to design such a classification:
–  by origin (European approach)
–  by purpose (American approach)
on commuting patterns but comply
with the administrative constraints
imposed by regional boundaries.
To structure the world of
enterprises, the SIRENE register
uses categories that reflect mandatory
reporting by firms and offer an outline
of “institutional sectors.” The General
Chart of Accounts (Plan Comptable
Général)—a central reference—is not
a statistical classification, although it
incorporates features requested by
statisticians. In France, corporate tax
returns for “income from industrial
and commercial activities” (bénéfices
industriels et commerciaux: BIC)
notably serve to prepare “intermediate
corporate
accounts”
(comptes
intermédiaires des entreprises), which
can be broken down by economic
activity.
National accounting, a representation
of economic flows, makes reference
to various classifications defined by
the United Nations System of National
Accounts (SNA 93) in the accounts of
institutional sectors: transactions in
goods and services, distribution-ofincome transactions, and financial
–  by intrinsic nature of products (as in
initial CPC).
Methodological advances have not
sufficed to settle the debate (Boeda et
al., 2002).
Data analysis
Instead of taking formal classification
structure as its starting point, data
analysis uses information on the objects
to be classified in order to deduce
aggregation classes and tree structures.
It assumes the existence of data, a
metric for the “distance” between two
objects, and a choice of levels for
aligning the tree-structure levels. The
classification obtained depends on the
data: any new information may call it
into question (Volle et al., 1970).
Area divisions for study purposes
routinely draw on data analysis. Its initial
applications have revealed relevant and
robust macroeconomic groupings. The
classification of sports activities has
relied on data analysis (Desrosières,
1972).
transactions. National accounting
also relies on classifications of
activities (for industry accounts) and
products (for supply-and-use tables)
as well as on functional classifications
for household consumption and
government expenditures. “Satellite
accounts” build bridges between
national accounting and various
sectors with specific classifications,
such as tourism, research, and
agriculture.
The health field (diseases, causes
of death, and so on) has its own
international statistical norms. It also
uses social-insurance management
tools
for
tracking
medical
procedures, medical and paramedical
occupations, and so on. The same is
true for education with UNESCO’s
International Standard Classification of
Education (ISCED) and management
tools used by French educational
district authorities (rectorats).
Classifications regarding individuals
(giving age, vital statistics, nationality,
and other characteristics) are used
by statisticians in the most neutral
manner possible. But they are primarily
The how and why of statistical classifications
administrative classifications subject
to various limitations with respect to
civil or penal legal age, number of
tax-deduction units per household,
and so on. Having been rejected by
the Constitutional Council, ethnicand religious-based typologies are
not used in France.
The customs classification, used
extensively by statisticians, clearly
illustrates the constraints of a
regulatory classification. Its goal is
to enable international trade to expand
in a transparent setting and to provide
a framework where rules can be
stated with their legal consequences.
Such rules apply to customs duties
and refunds, quotas, narcotics,
arms, hazardous products, and so
on. The first obligation, therefore, is
an unambiguous identification of all
merchandise, objectively observable
with state-of-the-art technology
(for example: traces of genetically
modified
organisms
[GMOs]).
Customs categories are therefore far
more focused on the boundaries of an
item than on its core—the opposite
of the statistician’s approach. Their
description may be either a very long
enumeration or a simple “other,” a
balancing item spelled out at the next
level of detail. Often, the economic
destination of products is of little
interest to customs authorities. The
statistician consequently interprets
“crawler tractor” as a construction
machine, a “wheeled tractor” as an
agricultural machine.
Statisticians may also be called in
to address a specific need. Three
very different examples—education/
training, waste, and physical
and sports activities—illustrate
“co-building” between classification
supply and demand, involving various
players and institutions.
The classification of education/
training specializations addresses
a long-latent need to reconstruct
a classification that had become
obsolete and mainly focused on
public education programs provided
in initial schooling. Technical training
programs were poorly represented
and, most importantly, lifelong
education for working adults was
Box 3: Naming, or why words count
The Swiss classification of activities had distinguished between—and therefore
named—metal roofing work as Bauspenglerei (German), travaux de ferblanterie
(French), and lavori di lattoneria (Italian): three languages, three different metals.
Moreover, in “French French,” ferblanterie would be replaced by zinguerie
(evoking zinc rather than tin)! This example shows that literal translation is not
always possible.
Translations from French into English and back again offer surprises: INSEE
had suggested adding “certification of civil-engineering structures” (in French:
certification des ouvrages d’art) to the explanatory notes for “technical inspection
services.” The translation came back as “authentication of works of art”
(authentification d’œuvres d’art).
In French, occupation can change with gender: the boulanger (“baker,” masculine)
kneads the dough and minds the oven, the boulangère (“baker,” feminine) serves
customers and operates the cash register. But the human brain is rather good
at decoding ambiguities: of the three expressions coupe de cheveux (“haircut”),
coiffeur (“hairdresser”) salon de coiffure (“hair salon”), only the first denotes an
activity; the second describes an occupation, and the third an establishment.
A likelihood test in a past population census had turned up a totally anomalous
number of farmers in urban areas, nearly all of them female. By checking the
sources, INSEE was able to identify the source of the anomaly: the occupation
jardinière d’enfants (“kindergarten worker,” feminine) had been shortened to
jardinière (“gardener,” feminine)—the watchword, at the time, was to save
computer processing space. The recurring error was easy to correct.
ignored. Via CNIS, INSEE has invited
representatives from the public
education system and the continuing
education system—two worlds that
usually do not work together—to sit
around the same table (Gensbittel et
al., 1992). A classification needs to
be negotiated; it cannot be forced on
users.
The classification of waste is a
result of the technical impossibility of
implementing the “European Waste
Catalogue” prepared by jurists. To put
it bluntly, the catalogue merely listed
economic activities and inserted
“waste from” before each. But many
types of waste are not generated by
activities. Examples include products
at the end of their life cycle, from
old documents to the French aircraft
carrier Clemenceau.
At Eurostat’s request, IFEN, ADEME,
INSEE, and a few international
experts formed a working group. It
defined waste categories by their
nature, ranking them by hazard where
applicable (chemical, radioactive
or biological), on the basis of
degradability or recyclability in other
cases. A secondary criterion was the
sequence of mandatory treatment
Courrier des statistiques, English series no. 15, 2009
stages for the waste flows: collection,
sorting, processing, and disposal.
The working group’s report was buried
for three years. It was resurrected as a
appendix to the 2002 EU regulation on
waste statistics, but with an artificial
linkage to the European Waste
Catalogue—which goes to show how
hard it is to abrogate a regulation.
The classification of physical and
sports activities was developed by
a working group composed of INSEE
and the statistical unit of the Ministry of
Youth Affairs and Sports (MJS, 2002).
A wide variety of data, supplementing
those of the 2000 Sports Participation
Survey, were “crunched” through the
ascending hierarchical classification
(AHC)
analysis
method.
The
project leader was responsible for
assigning weights to the different
data categories. The outcome was a
classification comprising 9 classes,
34 families, and 335 disciplines. While
the names of the disciplines are drawn
from standard sports terminology,
the groupings identified by the data
analysis are outright creations. Thus
the labels invented to describe them
mean nothing to people outside of the
working group. Good luck to these
new expressions!
5
Michel Boeda
Structural classifications:
activities and products
The customs model
Starting in the late 1960s, the European
Customs Union required Member
States to use national customs
classifications based on a “nesting”
European matrix. The only latitude
granted to individual countries was the
right to subdivide any European item
at the most detailed (“final”) level.
Formerly, each application program
was implemented using a specific
classification, for activities as well
as products. There was no clear
distinction
between
economic
activities and individual activities
(occupations). This tower of Babel
prevented full use of the information
available.
The
inter-ministerial
decree
promulgating NAP made its use
compulsory in official statistics.
It specified that the classification
by activity did not, in itself, create
rights or duties for firms. And it
reminded non-statistician users of
their own responsibility (see article
by Roussel).
The strictly national history of NAP
ended after twenty years of good
and faithful service (Lainé, 1999).
But customs classifications had
been sidelined—hence the lack of
consistency at detailed level between
the production and external-trade
spheres.
6
–  The French classification (NGP)
has a ninth position to express our
exceptions: wine, cheese, and so on.
These classifications evolve in
tandem, their regulatory purpose
leaving little room to accommodate
statisticians’ needs.
Source: Wikipedia
Modern times
The inter-departmental register
that preceded SIRENE created
an opportunity to impose the
classification of economic activities
(NAE 59). The national accounts—
most notably the input-output
table—provided a strong case for a
classification of products arranged
in the same way as the classification
of activities. At the same time, it
made sense to submit product
questionnaires to the firms that
carried the corresponding Principal
Economic Activity (APE) code. These
desiderata were fulfilled by the
“NAP 73” classification of activities
and products. As its name does
not indicate, it actually consisted of
a pair of mirror classifications with
600 matching items. The “products”
section was later refined in order to
adapt it to the “industry” surveys
and to begin the structuring of the
vast tertiary sector (NODEP: detailed
classification of products).
–  The next two allow a doubling of
detailed breakdowns (from 5,000 to
10,000 items) in the EU’s “Combined
Nomenclature” (CN) for the Common
Customs Tariff and external trade
statistics.
Russian dolls
This model has been systematized.
Since 1988, the same “Russian doll”
arrangement applies:
–  The first six digits of the customs
code are those of the Harmonized
System (HS).
The international and EU decision has
been to use the customs classifications
as the reference, which—in theory—
settles the issues of consistency
between the production sphere and
the external-trade sphere. Every good
is defined by a whole number of HS
positions at international level and by
a whole number of CN positions (if
needed) in Europe. There are some
adaptations, however. For example,
customs classifications recognize
only processed milk (a product of the
food industry) and ignore raw milk (a
product of livestock breeding) and
Box 4: Understanding the activities-products correspondence
Each activity generates characteristic products. Must every product originate
from a single activity? If we applied this principle to the lowest level of the
classification of activities, we would be assuming a nesting relation that would
make the product classification a sort of expanded version of the activity
classification. The U.N. Statistical Commission eventually decided to design the
CPC like the balance of payments.
Yet a concrete example brings the issue back to its proper proportions: in the
old CPF, the “production of fish” activity corresponded to the “fish” product.
But why deprive ourselves of the distinction between fishing and fish-farming
activities, which exhibit major differences such as employment at sea or on
land, processing equipment vs. boats, and resource management? Admittedly,
statisticians cannot discern fish (unless, perhaps, they are also gourmets).
We therefore have a product that is common to two activities at the detailed
level (coding linked to the higher level). Taking an ordinary activities-products
correspondence as our starting point, we had merely distinguished between
two modes of production for reasons of relevance to business statistics, without
impacting product statistics.
Retail trade offers a case that is more complex but open to the same analysis.
Merchandising consists in offering customers the products they want in the
right conditions. This is a service that justifies a profit margin. Each contract
lists the products sold (invoice), and retail trade is accordingly broken down by
product ranges sold. Retailing activity takes various forms, such as specialized
stores, non-specialized department stores, street markets, mail order, and online
vendors. Each form should be tracked, along with its effects on employment,
urban planning, and the social bond. Here, the activities-products relationship
takes the form of a matrix that cross-tabulates retailing methods and margins
per product range sold.
The how and why of statistical classifications
The Single European Market
The first European Community
classification of activities (NACE 70)
is contemporary with NAP 73, but
there is no one-for-one equivalence.
The prospect of a single market in
1993 required good comparability of
national statistics on the production
sector. The solution was a revised
NACE in which national classifications
would be nested.
The operation was carried out in
tandem with the third revision of
the International Standard Industrial
Classification of All Economic Activities
(ISIC), administered by the United
Nations—hence the same Russiandoll arrangement: ISIC Rev. 3 - NACE
Rev. 1 - NAF. Each is broken down in
detail in the next classification, but
the nesting is not visible in the code.
The operation has just been repeated,
in parallel with the fourth revision of
ISIC. This time, EU transparency has
been achieved. The present issue of
Courrier des statistiques is largely
devoted to the operation and its
impact on French statistics.
The national implementation of the
latest classification change reproduced
the initial procedure (Boeda, 1996),
but with better testing, supervision,
and documentation. The timetable
was tighter, as the statistical calendar
was now more Europeanized.
The first result of EU discussions
is the linkage between activities
and products, as advocated by
the French. This contributes to the
overall consistency with customs
classifications (see diagram on loose
sheet inserted in this issue).
Along with the demands of national
accountants, the decisive role fell to
statisticians in charge of industrial
statistics (Prodcom): to what should
one link a European list of several
thousand industrial goods, if not to
the activity code of the industry of
origin? Eurostat quickly understood
that the EU classification of products
would become an empty shell if it
failed to fit in between Prodcom and
NACE.
This
realization
led
to
the
establishment of the Classification
of Products by Activity (CPA). The
CPA code reproduces the NACE code
at aggregate levels, broken down
into two supplementary positions for
a detailed description, plus a twodigit position for the Prodcom list
(for goods-producing industries).
Box 5: The association criterion
The French theoretical approach is based on a correspondence between
activities and products and an association criterion. This prescribes a grouping
of activities (including to form an elementary “building block”) that respects the
associations most often encountered in units. Multiple activity is thus minimal
and the significance of the classification is maximal.
Underneath this empirical observation lies a microeconomic determinism. If the
market-entry cost of a key product is high (machinery, technology, research,
etc.), the firm that takes the step sets up a near-monopoly on the production that
depends on the key product. The firm has every incentive to press its advantage.
Conversely, the producer of an ordinary product, exposed to stiff competition, will
try to tailor the range to its customers, including as reseller. It is the combined set
of products and activities that develops its structure in the market: groupings are
shaped by a supply- or demand-driven rationale, as the case may be.
The association criterion, seldom articulated, informs discussions during revision
processes. For example, the latest revision saw the end of the centuries-old
association between printing and publishing, a separation between production
and repair of industrial goods, a confirmation of the association between trade
and repair of motor vehicles, and a convergence of multimedia activities.
Courrier des statistiques, English series no. 15, 2009
Source: Insee
many perishable products such as
fresh pastry. Experience has led to
a loosening of strict principles in the
latest revision of the classifications
(see article by Lacroix and Fuger).
French Classifications of Economic Activities and
Products, 1973 version (NAP 73)
In other words, this repeated the
NAP 73 arrangement, fleshed out by
NODEP and industry surveys. The
now larger majority of EU statistical
authorities has approved the CPA
structure, although the latest CPC
revision endorses its initial structure
and U.S. statisticians have defended
an alternative choice.
Macroeconomic classifications
Macroeconomic
analysis
must
operate on large, economically
significant categories, combining
market characteristics and corporate
strategy. For example, consumer
industries have to be accommodative
toward wholesalers and retailers, woo
customers, and segment the market;
by contrast, capital-goods industries
exploit their technical know-how
or that of a network of specialized
subcontractors by catering to the needs
of large customers. That is what the
“Summary Economic Classification”
(Nomenclature Économique de
Synthèse: NES) sought to capture
through its groupings, in contrast to
the ISIC/NACE groupings, which were
solely production-focused. Ultimately,
NES was adopted only in France,
whose statistical institute (INSEE)
7
Michel Boeda
displays the singular characteristic
of performing economic studies as
well. Another aim was to counter
non-coordinated groupings in official
statistics. The issue re-emerged in the
latest revision (see article by Madinier),
leading to an EU compromise that
involved the abandonment of NES
and officialized the dissemination of
statistics on different grouping levels.
Functional classifications
Beyond the production system, we
need to track the uses of products—
above all, household consumption.
The current international classification
is the Classification of Individual
Consumption by Purpose (COICOP:
only the English abbreviation is
used), with no EU or national
version. A conversion table shows
the correspondence with CPC (and
hence CPA/CPF). COICOP is used
for the Household Budget Survey—
conducted throughout the EU—and
to present the EU Harmonised
Index of Consumer Prices (HICP).
Purchasing power parities (PPPs)
between countries are determined by
means of a detailed breakdown of the
lowest COICOP level.
The Classification of the Functions
of Government (COFOG) is the
international system used to categorize
government expenditures. The latest
version, revised for consistency with
COICOP, is more specifically aimed at
breaking down general-government
final consumption (in the nationalaccounting sense) by category:
general administration, defense,
public order, education, health, social
protection, and so on. Individualconsumption items such as education
and health can thus be aggregated
with similar items financed directly by
households.
Structural classifications:
occupations and sociooccupational categories
France’s system of “Occupations
and Socio-Occupational Categories”
(Professions
et
Catégories
Socioprofessionnelles: PCS) succeeds
8
the “Socio-Occupational Categories”
(Catégories Socioprofessionnelles:
CSP), still used in everyday language.
This is a distinctly French development
(see article by Desrosières). The
very concept of social category—
introduced in the middle of the Cold
War—was bold. Technically, PCS
comprises two nested classifications:
occupations and socio-occupational
categories.
The basic rationale is that social identity
is built in the workplace. Occupation
is decisive for social positioning. It
is understood in the broad sense,
i.e., including job description, skills,
status, and terms of “collective
agreements” between employers
and employees in each industry. A
person’s occupation reflects his or
her education and training, family
background, and the context in which
(s)he engages in it. Income, lifestyle,
and consumption patterns go hand in
hand with occupation. The correlation
also applies to retired people—and
for households, so strongly does
endogamy persist in occupational
categories.
Econometricians therefore view the
social category as an overall indicator
that possesses a high explanatory
power when applied to household
behavior—and so eliminates the need
for multiple kinds of information that
are hard to access (such as income).
There is no comparable international
system: occupations lie within the
scope of the International Labor Office
(ILO), whereas social categories tend
to be the object of academic study.
By trying to promote convergence
between these fields, the European
Socio-economic Classification (EseC)
project is leading the way.
France has used PCS in censuses
since 1982, introducing a new version
in the 1999 census. A 2003 revision
concerned only the “Occupations”
section. The classification is used in
household surveys, while its variant
for employees (PCS-ESE, where
ESE stands for “Emploi Salarié en
Entreprise” [paid employment in firms])
is used for surveys or administrative
forms filed by employers.
At the same time as INSEE was
updating its national classification of
occupations, Eurostat was promoting
the application of the International
Standard Classification of Occupations
(ISCO, 1988 version). However, ISCO
was issued in a marginally adapted form
for Europe called ISCO(COM). This
venture registered some successes,
particularly in new Member States
with obsolete national classifications.
But an old ambiguity endures: ISCO
is focused not so much on people’s
occupations as on the jobs they hold
(see articles by Brousse and Torterat,
who notably discuss ISCO and its
European future).
PCS is very accurate if the protocol
is followed strictly. That is not so
easy a task, as it requires information
ranging beyond the job position. ISCO
is probably easier to code but leaves
a wider margin for interpretation.
The ILO expressly recognizes the
need for national classifications of
occupations, which should reflect
the structure of national employment
markets as faithfully as possible.
Work on ISCO 2008 is ending
without truly convincing results, all
the more so as it was performed
on an international scale and that
certain now-established EU practices
have been challenged, such as the
use of the category “administrative
managers in the public sector” (cadres
administratifs publics).
Absent an approved international
standard, social categorization
remains a strictly EU undertaking.
Eurostat had already been obliged to
recommend pseudo-social categories
(ISCO-based occupational groupings)
for EU Household Budget Surveys:
in so doing, it endorsed a founding
principle of the French PCS. The
theoretical inspiration for the current
project is Goldthorpe’s table of classes;
the project reference is the socioeconomic classification (ESeC: see
article by Brousse). The studies under
way seek to measure the prototype’s
capacity to capture occupations in
a PCS and/or ISCO framework and
to provide adequate explanatory
power in various applications of the
The how and why of statistical classifications
“common core” questionnaire in EU
household surveys.
Conclusion
Economic classifications are highly
standardized in the EU because the
process began long ago, and because
trade, technology, and the single
market all provided incentives in the
same direction (with reservations for
services, where local specificities
endure).
In the social sphere, the historical
legacy of particularisms is becoming
the rule. After half a century of
European convergence, reciprocal
recognition of education degrees has
not made much progress, and the
language barrier perpetuates heavy
labor-market segmentation.
The advantages of international
harmonization in the production
sphere vastly outweigh the drawbacks.
That argument is less self-evident
in the social sphere. Despite their
age, “tailor-made” national systems
remain attractive by comparison to an
off-the-shelf EU system that has not
yet found its bearings. n
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