Self-Archiving Impact Advantage: Quality Advantage or Quality Bias?

From: Stevan Harnad <>
Date: Mon, 20 Nov 2006 21:49:42 +0000

    Self-Archiving Impact Advantage: Quality Advantage or Quality Bias?

                 Stevan Harnad

    SUMMARY: In astrophysics, Kurtz found that articles that were
    self-archived by their authors in Arxiv were downloaded and cited
    twice as much as those that were not. He traced this enhanced citation
    impact to two factors: (1) Early Access (EA): The self-archived
    preprint was accessible earlier than the publisher's version (which
    is accessible to all research-active astrophysicists as soon as
    it is published, thanks to Kurtz's ADS system). (Hajjem, however,
    found that in other fields, which self-archive only published
    postprints and do have accessibility/affordability problems with
    the publisher's version, self-archived articles still have enhanced
    citation impact.) Kurtz's second factor was: (2) Quality Bias (QB),
    a selective tendency for higher quality articles to be preferentially
    self-archived by their authors, as inferred from the fact that the
    proportion of self-archived articles turns out to be higher among
    the more highly cited articles. (The very same finding is of course
    equally interpretable as (3) Quality Advantage (QA), a tendency for
    higher quality articles to benefit more than lower quality articles
    from being self-archived.) In condensed-matter physics, Moed has
    confirmed that the impact advantage occurs early (within 1-3 years of
    publication). After article-age is adjusted to reflect the date of
    deposit rather than the date of publication, the enhanced impact of
    self-archived articles is again interpretable as QB, with articles by
    more highly cited authors (based only on their non-archived articles)
    tending to be self-archived more. (But since the citation counts
    for authors and for their articles are correlated, one would expect
    much the same outcome from QA too.) The only way to test QA vs. QB
    is to compare the impact of self-selected self-archiving with
    mandated self-archiving (and no self-archiving). (The outcome is
    likely to be that both QA and QB contribute, along with EA, to the
    impact advantage.)

Michael Kurtz's papers have confirmed that in astronomy/astrophysics
(astro), articles that have been self-archived -- let's call this
"Arxived" to mark it as the special case of depositing in the central
Physics Arxiv -- are cited (and downloaded) twice as much as non-Arxived
articles. Let's call this the "Arxiv Advantage" (AA).

    Henneken, E. A., Kurtz, M. J., Eichhorn, G., Accomazzi, A., Grant,
    C., Thompson, D., and Murray, S. S. (2006) Effect of E-printing
    on Citation Rates in Astronomy and Physics. Journal of Electronic
    Publishing, Vol. 9, No. 2

    Henneken, E. A., Kurtz, M. J., Warner, S., Ginsparg, P., Eichhorn, G.,
    Accomazzi, A., Grant, C. S., Thompson, D., Bohlen, E. and Murray, S.
    S. (2006) E-prints and Journal Articles in Astronomy: a Productive
    Co-existence (submitted to Learned Publishing)

    Kurtz, M. J., Eichhorn, G., Accomazzi, A., Grant, C. S., Demleitner,
    M., Murray, S. S. (2005) The Effect of Use and Access on Citations.
    Information Processing and Management, 41 (6): 1395-1402

Kurtz analyzed AA and found that it consisted of at least 2 components:

(1) EARLY ACCESS (EA): There is no detectable AA for old articles in
astro: AA occurs while an article is young (1-3 years). Hence astro
articles that were made accessible as preprints before publication show
more AA: This is the Early Access effect (EA). But EA alone does not
explain why AA effects (i.e., enhanced citation counts) persist
cumulatively and even keep growing, rather than simply being a
phase-advancing of otherwise un-enhanced citation counts, in which case
simply re-calculating an article's age so as to begin at preprint
deposit time instead of publication time should eliminate all AA effects
-- which it does not.

(2) QUALITY BIAS (QB): (Kurtz called the second component
"Self-Selection Bias" for quality, but I call it self-selection Quality
Bias, QB): If we compare articles within roughly the same
citation/quality bracket (i.e., articles having the same number of
citations), the proportion of Arxived articles becomes higher in the
higher citation brackets, especially the top 200 papers. Kurtz
interprets this is as resulting from authors preferentially Arxiving
their higher-quality preprints (Quality Bias).

Of course the very same outcome is just as readily interpretable as
resulting from Quality Advantage (QA) (rather than Quality Bias (QB)):
i.e., that the Arxiving benefits better papers more. (Making a
low-quality paper more accessible by Arxiving it does not guarantee more
citations, whereas making a high-quality paper more accessible is more
likely to do so, perhaps roughly in proportion to its higher quality,
allowing it to be used and cited more according to its merit,
unconstrained by its accessibility/affordability.)

There is no way, on the basis of existing data, to decide between QA and
QB. The only way to measure their relative contributions would be to
control the self-selection factor: randomly imposing Arxiving on half of
an equivalent sample of articles of the same age (from preprinting age
to 2-3 years postpublication, reckoning age from deposit date, to
control also for age/EA effects), and comparing also with self-selected

We are trying an approximation to this method, using articles deposited
in Institutional Repositories of institutions that mandate
self-archiving (and comparing their citation counts with those of
articles from the same journal/issue that have not been self-archived),
but the sample is still small and possibly unrepresentative, with many
gaps and other potential liabilities. So a reliable estimate of the
relative size of QA and QB still awaits future research, when
self-archiving mandates will have become more widely adopted.

Henk Moed's data on Arxiving in Condensed Matter physics (cond-mat)
replicates Kurtz's findings in astro (and Davis/Fromerth's, in math):

    Moed, H. F. (2006, preprint) The effect of 'Open Access' upon citation
    impact: An analysis of ArXiv's Condensed Matter Section

    Davis, P. M. and Fromerth, M. J. (2007) Does the arXiv lead to
    higher citations and reduced publisher downloads for mathematics
    articles? Scientometics, accepted for publication.
    See critiques:

Moed too has shown that in cond-mat the AA effect (which he calls CID
"Citation Impact Differential") occurs early (1-3 years) rather than
late (4-6 years), and that there is more Arxiving by authors of
higher-quality (based on higher citation counts for their non-Arxived
articles) than by lower-quality authors. But this too is just as readily
interpretable as the result of QB or QA (or both): We would of course
expect a high correlation between an author's individual articles'
citation counts and the author's average citation count, whether the
author's citation count is based on Arxived or non-Arxived articles.
These are not independent variables.

(Less easily interpretable -- but compatible with either QA or QB
interpretations -- is Moed's finding of a smaller AA for the "more
productive" authors. Moed's explanations in terms of co-authorships
between more productive and less productive authors, senior and junior,
seem a little complicated.)

The basic question is this: Once the AA has been adjusted for the
"head-start" component of the EA (by comparing articles of equal age --
the age of Arxived articles being based on the date of deposit of the
preprint rather than the date of publication of the postprint), how big
is that adjusted AA, at each article age? For that is the AA without any
head-start. Kurtz never thought the EA component was merely a head
start, however, for the AA persists and keeps growing, and is present in
cumulative citation counts for articles at every age since Arxiving
began. This non-EA AA is either QB or QA or both. (It also has an
element of Competitive Advantage, CA, which would disappear once
everything was self-archived, but let's ignore that for now.)

    Harnad, S. (2005) OA Impact Advantage = EA + (AA) + (QB) + QA +
    (CA) + UA. Preprint.

Moed's analysis, like Kurtz's, cannot decide between QB and QA. The fact
that most of the AA comes in an article's first 3 years rather than its
second 3 years simply shows that both astro and cond-mat are
fast-developing fields. The fact that highly-cited articles (Kurtz) and
articles by highly-cited authors (Moed) are more likely to be Arxived
certainly does not settle the question of cause and effect: It is just
as likely that better articles benefit more from Arxiving (QA) as that
better authors/articles tend to Arxive/be-Arxived more (QB).

Nor is Arxiv the only test of the self-archiving Open Access Advantage.
(Let's call this OAA, generalizing from the mere Arxiving Advantage,
AA): We have found an OAA with much the same profile as the AA in 10
further fields, for articles of all ages (from 1 year old to 10 years
old), and as far as we know, with the exception of Economics, these are
not fields with a preprinting culture (i.e., they don't self-archive
prepublication preprints but only postpublication postprints). Hence
the consistent pattern of OAA across all fields and across articles of
all ages is very unlikely to have been just a head-start (EA) effect.

    Hajjem, C., Harnad, S. and Gingras, Y. (2005) Ten-Year
    Cross-Disciplinary Comparison of the Growth of Open Access and How
    it Increases Research Citation Impact. IEEE Data Engineering Bulletin
    28(4) pp. 39-47.

Is the OAA, then, QB or QA (or both)? There is no way to determine this
unless the causality is controlled by randomly imposing the
self-archiving on a subset of a sufficiently large and representative
random sample of articles of all ages (but especially newborn ones) and
comparing the effect across time.

In the meantime, here are some factors worth taking into account:

(1) Both astro and and cond-mat are fields where it has been repeatedly
claimed that the accessibility/affordability problem for published
postprints is either nonexistent (astro) or less pronounced than in
other fields. Hence the only scope for an OAA in astro and cond-mat is
at the prepublication preprint stage.

(2) In many other fields, however, not only is there no prepublication
preprint self-archiving at all, but there is a much larger
accessibility/affordability barrier for potential users of the published
article. Hence there is far more scope for OAA and especially QA (and
CA): Access is a necessary (though not a sufficient) causal precondition
for impact (usage and citation).

It is hence a mistake to overgeneralize the phys/math AA findings to OAA
in general. We need to wait till we have actual data before we can draw
confident conclusions about the degree to which the AA or the OAA are a
result of QB or QA or both (and/or other factors, such as CA).

For the time being, I find the hypothesis of a causal QA (plus CA)
effect, successfully sought by authors because they are desirous of
reaching more users, far more plausible and likely than the hypothesis
of an a-causal QB effect in which the best authors are self-archiving
merely out of superstition or vanity! (And I suspect the truth is a
combination of both QA/CA and QB.)

Stevan Harnad
Received on Mon Nov 20 2006 - 22:17:00 GMT

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