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    John Wiley & Sons http://www.jstor.org/stable/2486591.

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    Strategic Management Journal, Vol. 12, 167-185 (1991)

    HOW MUCH DOES INDUSTRYMATTER?

    RICHARD . RUMELT

    Anderson Graduate School of Management, University of

    California,

    Los

    Angeles,

    California, U.S.A.

    This study partitions

    the

    total

    variance

    in rate of return among FTC Line of Business

    reporting units into industry factors

    (whatever

    their nature),

    time

    factors, factors associated

    with the corporate parent,

    and

    business-specific factors.

    Whereas

    Schmalensee (1985)

    reported

    that

    industry factors

    were the

    stronlgest, corporate

    and

    market

    share

    effects being

    extremely weak, this study distinguishes between stable and fluctuating effects and reaches

    markedly different conclusions.

    The data

    reveal negligible corporate effects,

    small stable

    indlustryeffects,

    and

    very large

    stable business-unit

    effects. These results imlply that

    the most

    itnportant

    sources

    of

    economic rents

    are

    businiess-specific; ndustry membership

    is a

    much

    less

    itmportant

    ource and

    corporate parentage

    is

    quite unimportant.

    Because

    competition

    acts to

    direct

    resources

    towards uses

    offering the

    highest

    returns,

    persist-

    ently

    unequal

    returns mark the

    presence of

    either

    natural or

    contrived

    impediments to

    resource

    flows.

    The

    study of such

    impediments is a

    principal

    concern of

    industrial

    organization eco-

    nomics and

    the

    dominant unit of

    analysis

    in

    that field

    has been

    the

    industry. The

    implicit

    assumption

    has been

    that the

    most

    important

    market

    imperfections

    arise

    out

    of

    the

    collective

    circumstances

    and behavior

    of

    firms.

    However,

    the

    field of

    business

    strategy offers

    a

    contrary

    view: it

    holds that

    the most

    important

    impedi-

    ments

    are not

    the common

    property

    of

    collections

    of

    firms,

    but

    arise

    instead

    from the

    unique

    endowments

    and

    actions

    of

    individual

    corpo-

    rations

    or-

    business-units.

    If

    this is

    true, then

    industry

    may not

    be the

    most useful

    unit of

    analysis.

    Consequently,

    there should

    be

    consider-

    able

    interest in

    the relative

    sizes of

    inter-industry

    and

    intra-industry dispersions

    in

    long-term

    profit

    rates.

    Despite

    these

    arguments for

    this

    issue's sali-

    ence,

    surprisingly

    little work

    addressed

    it until

    Schmalensee's

    (1985)

    estimation of

    the

    variance

    components of

    profit

    rates in the

    FTC

    Line of

    Business

    (LB) data.

    Schmalensee

    decomposed

    0143-2095/91/030167-19$09.50

    ? 1991

    by

    John

    Wiley

    & Sons,

    Ltd.

    the total variance

    of

    rates

    of return on assets

    in

    the

    1975 LB data into

    industry,

    corporate,

    and

    market-share

    components. He reported that:

    (1)

    corporate

    effects did not exist; (2)

    market-share

    effects accounted

    for

    a

    negligible

    fraction

    of

    the

    variance in

    business-unit rates

    of return; (3)

    industry effects

    accounted for 20

    percent of the

    variance in

    business-unit returns;

    (4) industry

    effects accounted for at

    least 75

    percent

    of

    the

    variance in

    industry returns.'

    He concluded

    "the

    finding

    that

    industry effects are

    important

    supports the classical

    focus on

    industry-level

    analysis as against the

    revisionist

    tendency

    to

    downplay

    industry differences"

    (1985: 349).

    Schmalensee's

    study

    was

    innovative and

    techni-

    cally

    sophisticated.

    Nevertheless,

    there are

    diffi-

    culties with it traceable to

    the use of a

    single

    year of data.

    In

    this article

    I

    perform

    a new

    variance

    components analysis of

    the FTC LB

    data that corrects this

    weakness. I

    analyze the

    four years

    (1974-1977) of

    data available

    and

    '

    Industry and

    corporate

    'effects'

    are

    (unobserved) com-

    ponents of

    business-unit

    returns

    that are

    associated

    with

    membership

    in

    each

    particular

    industry

    and

    corporation. An

    'industry return'

    is the

    calculated

    average

    return of

    the

    business-units in that

    industry.

    Received 16 Februiary

    1990

    Revised 28 December

    1990

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    168

    R. P. Rumelt

    iniclude components for

    overall business cycle

    effects, stable

    and

    transient

    industry effects, as

    well as stable and transient business-unit effects.2

    Like Schmalensee, I find that corporate effects

    are negligible.

    However,

    I

    draw dramatically

    different conclusions about the importance of

    industry effects, the existence and importance of

    business-level effects,

    and the validity of industry-

    level analysis.

    The most

    straightforward

    way to review my

    analysis

    is to start

    with

    what

    Schmalensee's results

    left

    undecided.

    The first

    major incertitude is

    that,

    although 20 percent

    of

    business-unit returns are

    explained by 'industry effects',

    we

    do not know

    how much of this 20 percent is due

    to stable

    industry

    effects rather

    than

    to

    transient

    phenom-

    ena. For example, in 1975 the return on assets

    of the

    passenger

    automobile

    industry

    was 6.9

    percent

    and that of the

    corn wet

    milling industry

    was 35

    percent.

    But this

    difference was far from

    stable:

    in

    the

    following

    year

    the

    industries

    virtually reversed

    positions,

    auto's return

    rising

    to

    22.1

    percent

    and corn wet

    milling's

    return

    falling

    to 11.5

    percent

    (Federal

    Trade

    Com-

    mission,

    1975,

    1976).

    The presence

    of

    industry-

    specific fluctuations

    like these adds to the variance

    in

    industry

    returns observed

    in

    any

    one

    year.

    Thus, Schmalensee's snapshot estimate of the

    variance of 'industry effects' is the variance

    among

    stable

    industry

    effects

    plus

    the

    variance

    of annual fluctuations.

    But

    the 'classical

    focus' is

    surely

    on the

    stable differences among

    industries,

    rather

    than on

    random

    year-to-year

    variations

    in

    those differences.

    My analysis of

    the

    FTC

    LB

    data shows

    that

    stable

    industry effects

    account

    for only

    8

    percent of

    the

    variance

    in business-unit returns.

    Furthermore, only about 40 percent of the

    dispersion

    in

    industry

    returns

    is

    due

    to

    stable

    industry effects.

    The

    second incertitude concerns

    the

    variance not

    explained by industry

    effects.

    Schmalensee

    noted

    (p. 350)

    'it is

    important

    to

    recognize

    that

    80

    percent

    of

    the

    variance

    in

    business-unit

    2

    'Stable'

    industry effects are the (unobserved) time-invariant

    components of business-unit returns associated with member-

    ship in each industry. 'Stable'

    business-unit effects are the

    (unobserved) time-invariant components

    of business-unit

    returns that are not due to industry

    or corporate membership.

    profitability is unrelated

    to

    industry

    or share

    effects. While industry differences

    matter,

    they

    are clearly not all that matters.' If this

    intra-

    industry

    variance is due to

    transient

    disequilib-

    rium

    phenomena,

    then

    the 'classical focus on

    industry' would still be a contender; although it

    explains only 8 percent

    of

    the variance,

    it would

    be the only stable pattern in the data.

    But, if a

    large portion of the intra-industry variance is due

    to stable differences among business-units

    within

    industries, then the 'classical focus

    on industry'

    may

    be

    misplaced.

    In this

    study,

    I find that the majority of this

    'residual' variance is due to stable lotng-term

    differences among business-units rather

    than

    to transient phenomena. Using Schmalensee's

    sample,

    I

    find

    that stable

    business-unit

    effects

    account for 46 percent of the variance. Indeed,

    the stable business-unit

    effects

    are six times

    more

    important

    than

    stable

    industry effects

    in

    explaining

    the

    dispersion of

    returns. Business-

    units

    differ from

    one

    another withiin

    ndustries

    a

    great

    deal

    more

    than industries

    differ from

    one another.

    The

    conceptual conclusions are straightfor-

    ward. The 'classical focus on industry analysis'

    is mistaken because these industries are

    too

    heterogeneous to support

    classical

    theory.

    It

    is

    also mistaken because the most important

    impediments

    to

    the equilibration

    of long-term

    rates

    of return

    are

    not associated with industry,

    but with the

    unique endowments,

    positions,

    and

    strategies

    of individual businesses.

    The

    empirical warning

    is

    equally striking.

    Most

    of

    the observed

    differences

    among industry

    returns

    have

    nothing

    to do with

    long-term

    industry effects; they are due to the random

    distribution

    of

    especially high

    and

    low-performing

    business-units across industries.

    As will be

    shown,

    an FTC

    industry

    return

    must

    be

    at least 15.21

    percentage points

    above

    the

    mean to

    warrant a

    conclusion

    (95 percent confidence)

    that

    the true

    stable

    industry

    effect

    is

    positive.

    Fewer

    than

    one

    in

    forty industry returns

    are

    high enough

    to pass

    this test.

    BACKGROUND

    Most

    industrial

    organization

    research

    on

    business,

    corporate,

    and

    industry profitability

    tests

    prop-

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    How Much Does Industry

    Matter?

    169

    ositions about

    the causes of differential

    perform-

    ance. The primary tradition

    made industry

    the

    unit

    of analysis and sought

    a link between

    industry

    concentration (and

    entry barriers) and

    industry profitability

    (usually measured

    with

    pooled data).3 A second tradition focused on

    inter-firm

    differences in

    performance,

    seeking

    explanation

    first

    in

    terms

    of

    firm size and

    later

    in terms of market

    share.4 The early

    reaction

    against the mainline

    tradition viewed

    the concen-

    tration-profitability

    correlation as

    an artifact

    induced

    by the deeper

    share-profitability link.5

    Finally,

    the stochastic

    and

    efficiency

    views explain

    both

    firm

    profitability

    and market-share,

    and

    thus

    concentration,

    in terms of exogenous

    differential

    firm efficiencies.6

    In contrast to economics, business strategy

    research

    began with the presumption

    of hetero-

    geneity

    within industries

    and has

    only recently

    come to

    grips

    with

    the question

    of

    how differences

    in efficiency are

    sustained in the face

    of compe-

    tition. Thus,

    the earliest case research

    informed

    by the

    'strategy' concept focused

    on the different

    approaches

    to competition adopted

    by

    firms

    within

    the

    same industry.

    As the field matured,

    attention

    turned towards developing quantitative

    measures of

    this

    diversity7

    and,

    more

    recently,

    to its explanation in economic terms.8

    Each

    of

    these

    streams of

    work

    presumes

    different

    causal mechanisms

    and employs differ-

    ent units

    of

    analysis.

    Claims about whether

    profit-

    rate dispersion

    reflects collusion,

    share-based

    market power,

    or difficult-to-imitate

    resources

    are coupled with

    claims

    that the

    more

    aggregate

    phenomena

    are spurious

    or counter-claims

    that

    less

    aggregate

    phenomena

    are

    noise.

    My

    intention

    here

    is to

    suppress

    concern

    with causal mechan-

    isms

    and

    focus

    instead

    on the

    question

    of

    locus.

    Put differently, my concern here is with the

    existence

    and relative

    importance

    of

    time, corpo-

    rate,

    industry,

    and business-unit

    effects,

    however

    generated,

    on the

    total

    dispersion

    of

    reported

    rates

    of return.

    '

    See

    Weiss'

    (1974)

    survey of this line of

    work.

    4See

    Scherer's (1980)

    review of

    prior

    work on this

    topic.

    I

    Ravenscraft (1980,

    1983) is the best example of this line.

    6

    See Demsetz (1973)

    and Mancke (1974), as well as Lippman

    and Rumelt (1982).

    7Hatten

    and Schendel (1977) provided early contributions;

    see McGee and Thomas (1986) for a review

    of the strategic

    groups literature.

    8

    See Teece (1982),

    Rumelt (1984) and Wernerfelt (1984).

    Most

    prior

    work touching

    on the issue

    of locus

    has done so

    tangentially,

    rough

    measures

    of

    intra-

    industry

    dispersions

    in

    return being

    mentioned

    in passing

    within

    a study

    on a

    different

    topic.

    Stigler,

    for example, studying

    the

    convergence

    of profit rates over time, used the relative

    proportions

    of

    positive-profit

    and

    loss corpo-

    rations

    to

    construct rough

    estimates

    of

    intra-

    industry

    variances

    in the

    rate of

    return by

    IRS

    size class

    (his

    estimates

    unavoidably

    confound

    inter-period

    and

    inter-firm

    variances).

    He

    remarked

    in passing

    (1963:

    48) that these

    values

    were

    much larger

    than inter-industry

    variances,

    but

    drew no implications.

    Fisher

    and Hall (1969)

    measured

    the long-term

    (1950-1964)

    dispersion

    in

    rates of

    return

    about industry

    averages

    in

    order to obtain a measure of risk that could be

    regressed

    against

    industry

    profitability.

    Although

    they

    did not remark

    the fact,

    they

    obtained

    estimates

    that

    were

    approximately

    double their

    reported standard

    deviation

    in

    inter-industry

    rates

    of return.

    McEnally (1976),

    in an

    analysis

    of results

    obtained by

    Conrad

    and Plotkin

    (1968),

    showed

    that

    industries

    with

    larger

    average

    return

    tend

    also

    to have

    larger dispersions

    in

    long-term

    inter-

    firm rates

    of return.

    His figures9

    show inter-firm

    variances that are two to five times as large as

    inter-industry

    variances.

    As

    part

    of a re-examination

    of

    the

    concentration-profitability

    relationship,

    Gort

    and

    Singamsetti

    (1976)

    were

    apparently

    the

    first

    to

    explicitly

    ask

    whether

    or not 'the

    profit

    rates

    of

    firms cluster

    around

    industry

    means.'

    Assigning

    firms

    to

    3-digit

    and 4-digit

    industries, they

    found

    to their

    surprise

    that

    the

    data failed

    to

    support

    the

    hypothesis

    that

    industries

    have different

    characteristic

    levels

    of

    profitability.

    Furthermore,

    they noted that the proportion of the total

    variance explained

    by

    industry

    was low

    (approximately

    11

    percent.

    adjusted),

    did

    not

    increase

    as

    they

    moved

    from

    3-digit

    to

    4-digit

    industry

    definitions,

    and did not increase

    as

    the

    sample

    was restricted

    to

    more

    specialized

    firms.

    9

    Conrad

    and

    Plotkin computed intra-industry variances

    directly from deviations about industry averages. Because

    they

    are

    not based on

    true

    variance components estimation,

    their results may overestimate intra-industry variances and

    produce substantially upwards biased estimates of inter-

    industry variances (although the latter was not of direct

    interest to them or to McEnally).

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    170 R. P. Rumelt

    In

    an

    unpublished

    working paper

    I

    performed

    a

    variance components

    analysis

    of

    corporate

    returns

    using

    20

    years

    of

    Compustat

    data

    (Rumelt,

    1982).

    Although problems

    of

    industry definition

    and

    firm diversification prevented definitive

    results, here again the intra-industry effect

    dominated

    the

    inter-industry

    effect:

    the

    measured

    intra-industry

    variance in

    long-term

    firm

    effects

    was three

    to

    ten times as

    large as

    the

    variance

    due to industry-specific effects.

    Schmalensee's (1985)

    study

    was the

    first

    pub-

    lished

    work

    aimed

    squarely

    at

    these issues and

    is

    the direct ancestor of the

    work presented here.

    Looking

    at the

    1975 FTC

    LB

    data,

    Schmalensee

    estimated

    the

    following random-effects model:"'

    rik - +

    ,i

    +

    Pk

    +

    qSik

    +

    Eik

    (1)

    where

    rik

    is the

    rate

    of

    return of

    corporation

    k's

    activity

    in

    industry i,

    Sik

    is

    the

    corresponding

    market

    share,

    ai

    and

    Pk

    are industry and

    corporate effects

    respectively,

    and

    Eik

    is a

    disturbance. Schmalensee used

    regression

    to

    conclude that

    corporate effects

    were non-existent

    (Pk

    =

    0),

    and variance

    components

    estimation

    to

    show that

    industry

    effects

    were

    significant

    and

    substantial

    (Co2

    >

    0), and that share effects

    were

    significant but not substantial (-q

    >

    0 and

    uJ2 >

    q2or2)

    Kessides

    (1987)

    re-analyzed Schmalensee's

    data,

    excluding corporations

    active in

    less than

    three industries. He found

    statistically significant

    corporate

    effects in

    the restricted

    sample, suggest-

    ing

    that inclusion

    of the less-diversified

    corpo-

    rations had lowered

    the

    power

    of Schmalensee's

    test. In

    a

    related

    vein,

    Wernerfelt

    and

    Montgom-

    ery

    (1988)

    estimated

    a

    model

    patterned

    after

    Schmalensee's, replacing

    return on

    assets with

    Tobin's q and replacing the numerous corporate

    dummy

    variables with a

    single continuous meas-

    ure

    of

    'focus'

    (the

    inverse of

    diversification).

    They

    found

    industry

    effects and share

    effects of

    about

    the same

    magnitudes

    as

    Schmalensee

    found,

    and also

    found

    a

    small,

    but

    statistically

    significant,positive

    association

    between

    corporate

    focus

    and

    performance.

    Cubbin

    and

    Geroski

    (1987)

    attacked the

    question

    of the

    relative

    strength

    of

    industry

    and

    firm

    effects

    with a

    different

    methodology. Using

    "'

    I have

    altered his notation

    to preserve consistency

    within

    this paper.

    a sample

    of 217

    large U.K. firms, they measured

    how much of firms' profitability movements over

    time were unique, how much were related to

    other firms' movements, and how much were

    related to common industry movements. Nearly

    one-half of the companies in their sample

    exhibited

    no common

    industry-wide response

    to

    dynamic

    factors.

    Hansen

    and Wernerfelt

    (1989)

    studied the

    relative importance

    of

    economic and

    organi-

    zational

    factors

    in

    explaining

    inter-firm

    differences

    in profit

    rates.

    They

    found that

    industry explained

    19 percent

    of the variance in

    profit rates,

    but

    that organizational characteristics

    were

    roughly

    twice as important.

    DATA

    Because

    the

    impetus

    for

    this

    study comes

    from

    the existence

    of

    the

    unique

    FTC LB

    data,

    and

    because

    the statistical work

    performed

    is

    fundamentally descriptive rather than hypothesis

    testing,

    I

    break with

    convention and discuss

    the

    data

    before introducing

    the

    model.

    Data

    on the

    operations

    of

    large U.S. corpo-

    rations are

    available

    from a

    variety

    of

    sources.

    However, there is only one source of disaggregate

    data on

    the

    profits

    of

    corporations by industry-

    the

    FTC's

    Line

    of

    Business

    Program. The

    FTC

    collected

    data on

    the domestic

    operations

    of

    large corporations in each

    of

    261 4-digit FTC

    manufacturing industry categories.

    Information

    on a total

    of

    588

    different

    corporations was

    collected for the

    years 1974-1977;

    because of late

    additions, deletions, acquisitions,

    and

    mergers,

    the

    number

    of

    corporations reporting

    in

    any

    one

    year ranged

    from 432 to

    471. The average

    corporation reported on about 8 business-units.

    Schmalensee's

    sample

    was constructed

    by

    starting

    with Ravenscraft's

    (1983)

    data-set

    of

    3186 stable and

    meaningful

    business-units-those

    which were

    not

    in

    miscellaneous

    categories

    and

    which were neither

    newly

    created nor terminated

    during

    the

    1974-1976 period.

    He

    then dropped

    business-units

    in

    16

    FTC

    industries judged

    to

    be

    primarily residual classifications, dropped

    business-units

    with

    sales

    less

    than 1

    percent

    of

    1975 FTC

    industry total sales,

    and

    excluded one

    outlier.

    Two data

    sets were used in this research,

    labeled A and B.

    Sample

    A

    was constructed by

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    How

    Much

    Does

    Industry

    Matter?

    171

    starting

    with

    Schmalensee's sample of 1775

    business-units

    from

    the

    1975

    file and

    appending

    data

    on

    the same business-units from the 1974,

    1976,

    and

    1977 files. After this expansion, one

    business-unit

    was

    judged to have unreliable asset

    measures (in 1976-77) and was dropped. Eight

    other observations were eliminated because

    assets

    were reported as zero. Sample A then contained

    6932

    observations

    provided by 457 corporations

    on

    1774

    business-units

    operating

    in a total of 242

    4-digit FTC industries.

    Sample

    B was constructed

    by adding

    to

    Sample

    A the 1070 'small' business-units which had

    failed

    Schmalensee's size criterion.

    After

    adjoining

    the

    1974, 1976

    and

    1977 data

    for

    these business-

    units,

    34 were

    excluded

    due to

    (apparent)

    measurement problems: negative or zero assets,

    sales-to-assets

    ratios over

    30,

    and

    extreme

    year-

    to-year

    variations

    in

    assets that were

    unconnected

    to

    changes

    in

    sales. Sample

    B

    then contained

    10,866

    observations

    provided by

    463

    corporations

    on

    2810 business-units operating

    in

    a total

    of 242

    4-digit

    FTC industries.

    The rate of return was taken to

    be the ratio

    of

    profit

    before

    interest

    and taxes to

    total

    assets,

    expressed

    as

    a

    percentage.

    In

    sample

    A

    the

    average return

    was

    13.92 and the sample variance

    was 279.35. In sample B, the average and

    sample

    variance

    of

    return were

    13.17 and 410.73

    respectively.

    The FTC defined

    operating income

    as

    total

    revenues

    (including transfers

    from other

    units)

    less cost

    of

    goods sold,

    less

    selling, advertising,

    and

    general

    and administrative

    expenses.

    Both

    expenses

    and assets

    were further

    divided

    into

    'traceable'

    and

    'untraceable'

    components,

    the

    traceable

    component being directly

    attributable

    to

    the

    line of business and the

    untraceable

    component being allocated by the reporting

    firm

    among

    lines of

    business

    using

    'reasonable

    procedures.'

    In

    1975,

    15.8

    percent

    of the total

    expenses

    and 13.6

    percent

    of total

    assets

    of

    the

    average

    business-unit were

    allocated.

    A

    number

    of scholars have

    advanced

    arguments

    that

    accounting

    rates

    of return are

    systematically

    biased measures

    of

    true internal rates of return.

    I

    I

    Whatever the merits of this

    position,

    the

    purpose

    of this

    study

    is

    to

    partition

    the variance in

    reported

    business-unit rates of return. If

    different

    industry practices or corporate policies do induce

    "

    In particular, see Fisher

    and McGowan (1983).

    systematic biases in reported

    returns, the esti-

    mated variance components

    will reflect these

    facts and, therefore, help in

    estimating their

    importance.

    A

    VARIANCE COMPONENTS MODEL

    In discussing the heterogeneity

    within industries

    the term

    'firm' has an

    ambiguity that easily leads

    to

    confusion.

    In

    economics a 'firm'

    is usually an

    autonomous competitive unit within

    an industry,

    but the term

    is also

    often used

    to indicate a legal

    entity: a 'company'

    or

    'corporation'. Because

    most empirical studies are

    of

    large corporations,

    and because most

    large corporations

    are substan-

    tially diversified, legal or corporate 'firms' are,

    at

    best, amalgams

    of individual theoretical

    competitive units. Confusion

    can arise

    if

    one

    author uses the

    term 'firm effects' to indicate

    intra-industry dispersion

    among theoretical

    'firms',

    and another author uses the same term

    to

    denote

    differences

    among corporations

    which

    are not

    explained by

    their

    patterns

    of

    industry

    activities.

    To reduce the

    ambiguity

    in what follows

    I

    avoid the term

    'firm'.

    Instead,

    I use

    the term

    business-unit to denote that portion of a com-

    pany's operations

    which

    are wholly

    contained

    within a

    single industry.

    12

    I

    use the

    term

    corporation

    to

    denote

    a

    legal company

    which

    owns and operates one

    or

    more

    business-units.

    Thus,

    both industries

    and

    corporations

    are

    considered to

    be

    sets

    of

    business-units.

    In this

    regard,

    note

    that

    Schmalensee

    (1985)

    used

    the term 'firm-effects' to denote

    what I

    call

    corporate

    effects.

    Thus,

    his first

    proposition,

    'firm effects

    do not

    exist' (p. 349)

    refers

    to what

    are here termed corporate effects. Consequently,

    as he

    noted, finding insignificantcorporate

    effects

    does

    not rule out the

    presence

    of

    substantial

    intra-industry

    effects.

    However,

    unless more than

    one

    year

    of data are

    analyzed, intra-industry

    effects pool

    with

    the

    error and cannot be detected.

    Taking

    the

    unit of

    analysis

    to be the business-

    unit,

    assume

    that

    each business-unit is observed

    over

    time

    and is classified

    according

    to its

    industry

    12

    It is common practice

    among

    FTC

    LB researchers

    to

    refer

    to a business-unit as an 'LB'. I avoid this usage because

    many others

    naturally,

    but erroneously,

    believe that the term

    'Line

    of Business' refers

    to an industry group

    rather than to

    an individual

    business-unit

    within a larger firm.

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    172

    R.

    P.

    Rumelt

    membership and

    its

    corporate ownership. Let

    rik,

    denote the rate of return

    reported

    in

    time

    period

    t by the

    business-unit owned by corporation

    k

    and active in

    industry

    i. A

    particular

    business-

    unit

    is

    labeled ik, highlighting

    the fact that

    it

    is

    simultaneously a member of an industry and a

    corporation. Working

    with this

    notation,

    I

    posit

    the following descriptive model:

    rikt

    +

    -i

    +

    Pk

    +

    t

    +

    8it

    +

    ik

    +

    Eikt

    (2)

    where the

    (i

    are

    industry

    effects

    (i

    =

    1,

    I the

    Pk

    are corporate

    effects

    (k

    =

    1,

    . .

    .,

    the

    -y

    are

    year

    effects

    (t

    =

    1,

    . .

    .,

    L)

    the

    sit

    are industry-year interaction

    effects

    (l distinct

    it

    combinations),

    and the

    4ik

    are business-unit

    effects (4,, distinct ik combinations). The

    Eikt

    are

    random disturbances

    (one

    for each of

    the

    N

    observations).

    Each

    corporation

    is

    only

    active in

    a

    few

    industries,

    so

    l,