Does Collocation Inform the Impact of Collaboration?
Kyungjoon Lee1
, John S. Brownstein2
, Richard G. Mills3
, Isaac S. Kohane1,2
*
1 Center for Biomedical Informatics, Harvard Medical School, Boston, Massachusetts, United States of America, 2 Children’s Hospital Informatics Program at the HarvardMIT
Division of Health Sciences and Technology, Boston, Massachusetts, United States of America, 3 Operations and Business Affairs, Harvard Medical School, Boston,
Massachusetts, United States of America
Abstract
Background: It has been shown that large interdisciplinary teams working across geography are more likely to be impactful.
We asked whether the physical proximity of collaborators remained a strong predictor of the scientific impact of their
research as measured by citations of the resulting publications.
Methodology/Principal Findings: Articles published by Harvard investigators from 1993 to 2003 with at least two authors
were identified in the domain of biomedical science. Each collaboration was geocoded to the precise three-dimensional
location of its authors. Physical distances between any two coauthors were calculated and associated with corresponding
citations. Relationship between distance of coauthors and citations for four author relationships (first-last, first-middle, lastmiddle,
and middle-middle) were investigated at different spatial scales. At all sizes of collaborations (from two authors to
dozens of authors), geographical proximity between first and last author is highly informative of impact at the microscale
(i.e. within building) and beyond. The mean citation for first-last author relationship decreased as the distance between
them increased in less than one km range as well as in the three categorized ranges (in the same building, same city, or
different city). Such a trend was not seen in other three author relationships.
Conclusions/Significance: Despite the positive impact of emerging communication technologies on scientific research, our
results provide striking evidence for the role of physical proximity as a predictor of the impact of collaborations.
Citation: Lee K, Brownstein JS, Mills RG, Kohane IS (2010) Does Collocation Inform the Impact of Collaboration? PLoS ONE 5(12): e14279. doi:10.1371/
journal.pone.0014279
Editor: Christos Ouzounis, King’s College London, United Kingdom
Received July 15, 2010; Accepted November 4, 2010; Published December 15, 2010
Copyright: ß 2010 Lee et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was supported by the Kauffman Foundation and the Office of the Provost at Harvard University. The funders had no role in study design,
data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: isaac_kohane@harvard.edu
Introduction
As scientific research becomes increasingly complex, investigations
frequently involve large-scale collaborations and multidisciplinary
teams [1]. A growing range of communication
technologies including email, instant messaging, intranets, wikis,
and document sharing systems, are enabling distributed, instantaneous
scholarly collaboration irrespective of location. There
have been several recent publications on the impact of ‘‘big
science’’ and large interdisciplinary teams [2,3,4]. The overall
message of these publications is that large teams of investigators,
especially those working together irrespective of geography (e.g.
international consortia) are more likely to be impactful. Understanding
the fundamental relationship between collaborator
proximity and scientific impact can improve the planning of
educational and research facilities and guide the optimal design of
large-scale research collaborations.
Results
Figure 1 shows that citation of an article has strong positive
correlation with the number of coauthors. This trend becomes
obvious for articles with more than 5 authors. Because of this, to
see the relationship between author distance and citation, articles
with different number of coauthors need to be analysed separately.
We separated articles with 4 or less authors and 5 or more authors
in the subsequent analysis.
As Harvard authors are in four major locations (Longwood
Medical Area, Massachusetts General Hospital (MGH) main
campus, MGH Navy Yard campus, and McLean Hospital), the
distance between coauthors are aggregated in discrete values
(Figure 2). Maximum values (12 km) between coauthors are for
authors in MGH campuses and McLean Hospital. Most of these
authors collaborated with people within 200 m (Figure 3).
Figure 4 shows coauthor distance and mean citation for all four
author relationships within an article: first-last (FL), first-middle
(FM), last-middle (LM), middle-middle (MM). While there is only
one FL in any article, there are (n-2) FMs or LMs in an article with
n authors, and (n-2)6(n-3)/2 MMs. FM/LM/MM graphs show
that the ALL graphs are dominated by . = 5 data because there
are many more same relationship pairs as n increases. If there is an
article with 100 coauthors and 50 citations, for example, the
citation 50 gets counted 98 times in FM/LM mean citation and
,10000 times in MM. There is one safe case, though. If there are
4 authors, there is only 1 MM. If there are less than 4 authors,
there is no MM. Therefore, graphs for FL and MM, = 4 are safe
for interpretation. Other graphs should be interpreted carefully.
Figures 5A and 7 show significant relationships between
proximity and impact: the closer the first and last author, the
greater the number of citations, an effect that is not evident
PLoS ONE | www.plosone.org 1 December 2010 | Volume 5 | Issue 12 | e14279
between middle authors (Figure 6). Figure 8 shows that buildings
with a higher-proportion of publications resulting from intrabuilding
collaborations (as opposed to inter-building collaborations)
also tend to have higher mean citations among all
publications with at least one author working in the building
(r = 0.50, n = 87, p-value = 1.061026 by Spearman’s rank
correlation test).
Discussion
The results of this first-of-a-kind study suggest that although
emerging communication technologies have radically transformed
the style and scope of collaboration around the world, physical
proximity continues to play a critical role in predicting the impact
of scientific research. Although causal relationships cannot be
inferred from observational data, a few important associations can
be identified. First physical proximity of collaborators was found to
be positively associated with publication impact. This effect is most
notable for proximity between first and last authors and was not
found for other author combinations. Second, the level of intrabuilding
collaboration is positively associated with the impact of
publications originating in that building.
There are a number of possible explanations for these
associations. It may be that physical proximity truly allows for
better collaboration, resulting in higher quality research that tends
to be cited more often. It may also be that investigators have a
strategic preference for keeping potentially high impact projects
wholly within their own laboratory or close circle of research
associates.
There have been numerous articles [5] that reported Open
Access publications have higher chance to be cited more. It may
be that publications in Open Access journals have higher citation,
which may not necessarily be related to collaboration and
collocation. However, its impact on our results is uncertain as
there are also growing number of articles that are reporting no
evidence of Open Access advantage [6,7] in different disciplines.
Previous studies [4] have found that publications arising from
international collaborations are associated with greater citation
impact than those arising from local collaborations. In this study,
we examined the effect of pair-wise inter-collaborator distance
within a local framework and found that impact increases with
proximity. Therefore advising or make an institutional policy to do
international collaboration may not just work at the individual
level. It might be more effective to guide faculty to arrange space
so that there are more direct interaction with the students and
postdocs.
Figure 1. Number of coauthors and mean citations. Citation of an
article has strong positive correlation with the number of coauthors.
This trend becomes obvious for articles with more than 5 authors.
Because of this, to see the relationship between author distance and
citation, articles with different number of coauthors need to be
analysed separately. We separated articles with 4 or less authors and 5
or more authors.
doi:10.1371/journal.pone.0014279.g001
Figure 2. Scatter plot of distance between authors and citation
for high resolution data. High resolution data is only available for
Harvard affiliated authors. Harvard authors are in 4 major geographical
locations: Longwood Medical Area, Massachusetts General Hospital (MGH)
main campus, MGH Navy Yard campus, and McLean Hospital. Distances
between authors are aggregated in discrete values because authors are
not uniformly distributed but in one of those 4 locations. Maximum value
(12 km) are for authors in MGH campuses and McLean Hospital.
doi:10.1371/journal.pone.0014279.g002
Figure 3. Histogram of data in Figure 2. Most of the coauthors are very close to each other within 200 m.
doi:10.1371/journal.pone.0014279.g003
Collocation and Collaboration
PLoS ONE | www.plosone.org 2 December 2010 | Volume 5 | Issue 12 | e14279
Figure 4. Distance and mean citation in different author relationships. There are four author relationships within an article: first-last, firstmiddle,
last-middle, middle-middle. While there is only one FL in any article, there are (n-2) FMs or LMs in an article with n authors, and (n-2)x(n- 3)/
2 MMs. As you can see in FM/LM/MM graphs, the ALL graphs are dominated by . = 5 data because there are way more same relationship pairs as n
increases. If there is an article with 100 authors/50 citations, for example, the citation 50 gets counted 98 times in FM/LM mean citation and ,10000
times in MM. There is one safe case, though. If there are 4 authors, there is only 1 MM. If there are less than 4 authors, there is no MM. Therefore,
graphs for FL and MM , = 4 are safe for interpretation. Other graphs should be interpreted carefully.
doi:10.1371/journal.pone.0014279.g004
Collocation and Collaboration
PLoS ONE | www.plosone.org 3 December 2010 | Volume 5 | Issue 12 | e14279
Figure 5. Distance and mean citation for first-last author relationship in three resolutions (100 m, 1 km, and 1000 km).
doi:10.1371/journal.pone.0014279.g005
Figure 6. Distance and mean citation for middle-middle author relationship in articles with less than 5 coauthors in three
resolutions (100 m, 1 km, and 1000 km). There is no obvious trend.
doi:10.1371/journal.pone.0014279.g006
Collocation and Collaboration
PLoS ONE | www.plosone.org 4 December 2010 | Volume 5 | Issue 12 | e14279
Further work is needed to more deeply understand these
relationships and to validate these results across multiple
institutions, historical periods, fields of study and measures of
scientific productivity. It is possible that these results are only valid
for institutions that have similar organizational structure as
Harvard University where most of the faculties are appointed to
Harvard Medical School as well as one of the totally independent
affiliated hospitals. It may be that this unique organizational
structure defined the scientific sub-community, which is reflected
as collocation.
It is also possible that these results are unique to biomedical
sciences. Therefore, it would be necessary to validate these results
using other bibliographic databases in other discipline such as the
Association for Computing Machinery’s (ACM) Digital Library
and IEEE’s Xplore Digital Library.
Materials and Methods
As part of our CoCo (collocation-collaboration) project, we
analyzed the relationship between collaborator proximity and
scientific impact as measured by publication citations. We
assembled an unprecedented high-resolution geographic record
of scientific collaboration based on the individual offices and
laboratories of researchers in a large academic centre.
Figure 7. Mean citation for first-last authors in the same
building, same city, or different city. Scatter plot showing
relationship between first author-last author distance and publication
citation impact (62 SEM). Three inter-author distances were selected for
illustration: same building, same city or different cities. Results are
plotted for publications with four or fewer authors (black), and with five
or more authors (red).
doi:10.1371/journal.pone.0014279.g007
Figure 8. 3-D representation of the relationship between intra-building collaboration and mean citation impact on the Longwood
campus of Harvard Medical School. The height of each building reflects the mean number of citations of publications originating in that
building, and the color gradient reflects the proportion of publications originating from that building in which both first and last authors work in the
building (from grey = low to blue = high). An interactive version of this map could be found at http://collaboration.harvard.edu.
doi:10.1371/journal.pone.0014279.g008
Collocation and Collaboration
PLoS ONE | www.plosone.org 5 December 2010 | Volume 5 | Issue 12 | e14279
We focused on life sciences research across three major Harvard
University campuses: the Faculty of Arts and Sciences campus in
Cambridge, the Longwood campus of Harvard Medical School
and the Cambridge and Boston campuses of Massachusetts
General Hospital. We analyzed all PubMed-indexed publications
with at least one Harvard author published in the years 1999
through 2003, for a total of 35,000 articles across 2,000 journals by
200,000 authors. Since author affiliations were only listed at the
institutional level, we performed detailed geo-historical investigation
to identify and pinpoint the three-dimensional office location
of each author in each specific year.
To study the effect of collaboration size, we divided the
publications into those with four or fewer authors and those with
five or more. Because of the traditionally privileged roles attributed
to first and last authors in the biomedical literature, we highlighted
the effect of distance particularly for these author positions and
compared them to middle authors.
Acknowledgments
We thank Adam Aroesty-Cohen, Christopher Lafortune, Devorah Edison,
Jonathan Packer, Judah Leeder, Kerry Foley, Laura Roth, Marika
Feuerstein, Marika Osterbur, Melissa McCue, Patsy Foley, Ross Eisenberg,
Sam Israel, and Tony Berbara for the data collection, Scott Lapinski,
Elizabeth Eggleston, Susan Vomacka, and Jennifer Galbraith for providing
the Harvard office location information of the individuals, Richard
LeBlanc for providing the Harvard building information.
Author Contributions
Conceived and designed the experiments: KL ISK. Performed the
experiments: KL. Analyzed the data: KL JB ISK. Contributed reagents/
materials/analysis tools: KL RGM ISK. Wrote the paper: KL JB ISK.
References
1. Wuchty S, Jones BF, Uzzi B (2007) The increasing dominance of teams in
production of knowledge. Science 316: 1036–1039.
2. Redon R, Ishikawa S, Fitch KR, et al. (2006) Global variation in copy number in
the human genome. Nature 444: 444–454.
3. Jones BF, Wuchty S, Uzzi B (2008) Multi-university research teams: shifting
impact, geography, and stratification in science. Science 322: 1259–1262.
4. Bordons M, Go´mez I, Ferna´ndez MT, Zulueta MA, Me´ndez A (1996) Local,
domestic and international scientific collaboration in biomedical research.
Scientometrics 37: 279–295.
5. Craig ID, Plume AM, McVeigh ME, Pringle J, Amin M (2007) Do open access
articles have greater citation impact? A critical review of the literature.
J Informetrics 1: 239–48.
6. Davis PM, Lewenstein BV, Simon DH, Booth JG, Connolly MJ (2008) Open
access publishing, article downloads, and citations: randomised controlled trial.
BMJ 337: a568.
7. Calver MC, Bradley JS (2010) Patterns of citations of open access and non-open
access conservation biology journal papers and book chapters. Conserv Biol 24:
872–80.
Collocation and Collaboration
PLoS ONE | www.plosone.org 6 December 2010 | Volume 5 | Issue 12 | e14279