Scientometricians have devoted much time to the analysis of the (almost mythical) relation between collaboration and citation impact. Several authors found positive correlation between collaboration and scientific productivity (Price and Beaver, 1966; Beaver and Rosen, 1979, Braun et al., 2001, Glänzel, 2002). These findings were extended by including also citation indicators to establish a relation between collaboration and impact or visibility of scientific output (Glänzel & Schubert, 2001; Schmoch & Schubert, 2008). Other authors investigated collaboration patterns in specific fields or disciplines (Bordons et al. 1996, Gomez, et al., 1999) or in a specific institute (Iribarren-Maestro et al., 2009).In the present study we investigate the relation between multi-authorship and citation impact. We will not only look at the correlation between both variables but also take other sources of variations (e.g., fields, journals, countries) that might have an influence on the impact of research. In order to be able to assess the influence of the different fields on the observed results we introduce a new measure to calculate the average number of authors by a field. This measure can then be used as an expectation for the number of author for a particular paper. Thus the Expected Author Rate (EAR) is defined as the average number of authors for an entity like journals or fields in a given year. This can be correlated with citation indicators. We observed for the 61 relevant fields a strong correlation between the expected citation rate and the average number of authors. We also applied different regression analysis to assess the influence of number of authors on citation indicators at different levels of aggregation: journals, institutions and countries. After correction with the EAR the analyses showed no effect of number of authors.

1. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Multi-authorship and citation
advantages:
A mythical relationship
Bart Thijs1
Rodrigo Costas2
Wolfgang Glänzel1,3
1. ECOOM, Katholieke Universiteit Leuven, Belgium
2. Leiden University, Centre for Science and
Technology Studies (CWTS), Netherlands
3. Institute for Research Policy Studies, Hungarian
Academy of Sciences, Budapest, Hungary

2. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Introduction
The study of the relation between collaboration
among scientists and research output has a long
tradition.
• Collaboration and production
– Price & Beaver, 1966
– Beaver & Rosen, 1979
– Braun et al. 2001
– Glänzel, 2002

3. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Introduction
• Collaboration and Citations
– Glänzel & Schubert, 2001 and Glänzel, 2001
– Schmoch & Schubert, 2008
• Collaboration patterns in specific fields or
institute
– Bordons et al., 1996
– Gomez et al., 1999
– Iribarren-Maestro et al., 2009

4. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Introduction
In this study we investigate the relation between
collaboration and citation scores.
We introduce a methodology to normalize
measurements of multi-authorship and
international collaboration in order to be able to
investigate the relation in absence of field
specific effects.
These normalized measures are applied on three
different levels of aggregation: journals,
countries and institutes.

5. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Data
• SCIE,SSCI from Thomson-Reuters
• Publications from the annual updates 1998-
2007
• Only citable document type: Article, Letter,
Proceedings Paper or Review
• 3 year citation window is used
• Leuven-Budapest classification = Journal
based field/discipline classification

6. COLLNET 2011,
September 20-23,
Istanbul, Turkey
First observations
0
1
2
3
4
5
6
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Multi
Single
Multi authored
papers have more
citations than
single authored
papers
The difference between multi and single
papers remains constant over time.

7. COLLNET 2011,
September 20-23,
Istanbul, Turkey
First observations
Same observations
applies for countries.
Papers with
international
collaboration have
on average more
citations than
domestic papers.
0
1
2
3
4
5
6
7
8
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Internat.
Domestic

8. COLLNET 2011,
September 20-23,
Istanbul, Turkey
First observations
0
5
10
15
20
25
30
35
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Countries
Authors
Average number of citations increases with
growing number of authors/countries.
Kendall t
Countries 0.15
Authors 0.21

9. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Conclusions?
Can we conclude based on these three graphs
that more authors/countries leads to more
citations?
More than … what?

10. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Role of fields
• Research field plays a important role on the
behaviour of scientists.
• Different fields act like different communities
or even like different cultures.
0
0.1
0.2
0.3
0.4
0.5
0.6
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Authors
Countries
High rank correlation
between authors
and citations across
62 fields.

11. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Central tendency
More than ….?
…the average within the field.

12. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Central tendency
The use of expected citation rates are very
common in bibliometrics.
Analogue to these we can define an
• Expected Author Rate
• Expected Country Rate
More than ….?
…the average within the field.

13. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Definitions
The Expected Author Rate for a field (EARf) is
the average number of authors over all papers
that are in full or partially assigned to the field
within one year. Papers with multiple field
assignments are fractionated and only partially
counted both in numerator and denominator.
The Expected Author Rate for a journal (EARj) is
the average number of authors over all papers in
a journal within one year.

14. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Definitions
EAR and ECntrR provides us with reference
standards for collaboration both for fields and for
journals.
As with citations we can calculate a relative
indicator that shows us whether a paper (or set of
papers) has more or less authors than we might
expect based on the reference standard
Normalized Author Rate =
Observed Number of Authors
Expected Author Rate

15. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results
The relation between collaboration and citation
indicators will be investigated at three different
levels of aggregation
• Journals
• Countries
• Institutes
Publications from 2005 to 2007
Al least 100 publications over three year period

16. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Journals
Kendall’s t Average Citations
Expected Citation Rate Field 0.35
Average Number of Authors 0.35
Expected Authors Rate Field 0.28
Average Number of Countries 0.30
Expected Country Rate Field 0.15
Normalized Citation Rate Field 0.60
Normalized Author Rate Field 0.22
Normalized Country Rate Field 0.25
The average number of citations within journals has a significant
positive rank correlation with all 8 other indicators. The highest
correlation can be found with the Normalized Citation Rate for
the field

17. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Journals, field normalized
Kendall’s t Normalized citation rate
Expected Citation Rate Field -0.05**
Average Number of Authors 0.12
Expected Authors Rate Field -0.05**
Average Number of Countries 0.35
Expected Country Rate Field 0.04**
Normalized Author Rate Field 0.27
Normalized Country Rate Field 0.38
The average number of citations within journals has a significant
positive rank correlation with 4 other indicators. All Expected
Rates do not rank correlate. The underlined correlations are even
higher than in the previous analysis.

18. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Journals, field normalized
Stepwise regression Step Status Coeff P-value
Average Number of Authors Out -0.016 0.07
Average Number of Countries 3 In 0.35 0.0004
Normalized Author Rate Field 2 In 0.30 0.0000
Normalized Country Rate Field 1 in 1.07 0.0000
In a stepwise regression, the average number of authors is not
entered in the model. The relation between the normalized rates
holds. Also the average number of countries involved in papers
explains additional variance in the regression model. We can
conclude that journals that have papers with more
authors/countries than we might expect based on their field also
have more citations than we expect.

19. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Countries
Kendall’s t Average Citations
Expected Citation Rate Journal 0.78
Expected Citation Rate Field 0.60
Relative Citation Rate (RCR) 0.56
Mean Normalized Citation Rate (NMCR) 0.71
ECRj/ECRf = NMCR/RCR 0.54
Average Number of Authors 0.43
Expected Authors Rate Journal 0.56
Expected Authors Rate Field 0.51
Normalized Author Rate Journal 0.21
Normalized Author Rate Field 0.29
Average Number of Countries 0.15
Expected Country Rate Journal 0.17
Expected Country Rate Field 0.07
Normalized Country Rate Journal 0.12
Normalized Country Rate Field 0.14
The average number
of citations in
countries shows
significant rank
correlations with all
15 available
indicators. Those
indicators related to
citations show the
highest correlations.

20. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Countries
Kendall’s t Average Citations RCR NMCR
Expected Citation Rate Journal 0.78 0.35 0.56
Expected Citation Rate Field 0.60 0.28 0.31
Relative Citation Rate (RCR) 0.56 1.00 0.64
Normalized Mean Citation Rate (NMCR) 0.71 0.64 1.00
ECRj/ECRf = NMCR/RCR 0.54 0.30 0.66
Average Number of Authors 0.43 0.30 0.34
Expected Authors Rate Journal 0.56 0.33 0.38
Expected Authors Rate Field 0.51 0.30 0.28
Normalized Author Rate Journal 0.21 0.21 0.21
Normalized Author Rate Field 0.29 0.25 0.30
Average Number of Countries 0.15 0.13 0.17
Expected Country Rate Journal 0.17 0.06 0.22
Expected Country Rate Field 0.07 -0.05 0.09
Normalized Country Rate Journal 0.12 0.14 0.12
Normalized Country Rate Field 0.14 0.15 0.16

21. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Countries – Stepwise Regression
Stepwise regression - RCR Step Status Coeff P-value
ECRj/ECRf = NMCR/RCR 1 In 0.5248 0
Average Number of Authors Out 0.7462
Expected Authors Rate Journal Out 0.6761
Expected Authors Rate Field Out 0.2481
Normalized Author Rate Journal Out 0.5329
Normalized Author Rate Field Out 0.7998
Average Number of Countries Out 0.9034
Expected Country Rate Journal Out 0.5138
Expected Country Rate Field 2 In 1.0536 8.60E-03
Normalized Country Rate Journal Out 0.9003
Normalized Country Rate Field Out 0.9324

22. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Countries – Stepwise Regression
Stepwise regression - NMCR Step Status Coeff P-value
ECRj/ECRf = NMCR/RCR 1 In 1.4958 0
In the stepwise regression, the ratio between the two expected
citation rates takes a prominent role.
For countries it is safe to conclude that those who score high on
normalized citation indicators also tend to publish more in
journals that have higher expected citations rates than the field
in which they are active.

23. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Institutes
Kendall’s t Average Citations
Expected Citation Rate Journal 0.78
Expected Citation Rate Field 0.40
Relative Citation Rate (RCR) 0.65
Mean Normalized Citation Rate (NMCR) 0.90
ECRj/ECRf = NMCR/RCR 0.75
Average Number of Authors 0.40
Expected Authors Rate Journal 0.47
Expected Authors Rate Field 0.23
Normalized Author Rate Journal 0.32
Normalized Author Rate Field 0.38
Average Number of Countries 0.26
Expected Country Rate Journal 0.40
Expected Country Rate Field 0.17
Normalized Country Rate Journal 0.23
Normalized Country Rate Field 0.26
The average number
of citations in
institutes shows
significant rank
correlations with all
15 available
indicators. Those
indicators related to
citations show the
highest correlations.

24. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Institutes
Kendall’s t Average Citations RCR NMCR
Expected Citation Rate Journal 0.78 0.35 0.56
Expected Citation Rate Field 0.40 0.28 0.31
Relative Citation Rate (RCR) 0.65 1.00 0.64
Mean Normalized Citation Rate (NMCR) 0.90 0.64 1.00
ECRj/ECRf = NMCR/RCR 0.75 0.30 0.66
Average Number of Authors 0.40 0.30 0.34
Expected Authors Rate Journal 0.47 0.33 0.38
Expected Authors Rate Field 0.23 0.30 0.28
Normalized Author Rate Journal 0.32 0.21 0.21
Normalized Author Rate Field 0.38 0.25 0.30
Average Number of Countries 0.26 0.13 0.17
Expected Country Rate Journal 0.40 0.06 0.22
Expected Country Rate Field 0.17 -0.05 0.09
Normalized Country Rate Journal 0.23 0.14 0.12
Normalized Country Rate Field 0.26 0.15 0.16

25. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Institutes – Stepwise Regression
Stepwise regression / RCR Step Status Coeff P-value
ECRj/ECRf = NMCR/RCR 2 In 0.3038 0
Average Number of Authors Out 0.9712
Expected Authors Rate Journal Out 0.3423
Expected Authors Rate Field 1 In 0.1302 0
Normalized Author Rate Journal Out 0.5179
Normalized Author Rate Field 5 In -0.0176 0
Average Number of Countries Out 0.0282
Expected Country Rate Journal Out 0.0375
Expected Country Rate Field 3 In -0.4312 0
Normalized Country Rate Journal 4 In 0.2217 0
Normalized Country Rate Field Out 0.023

26. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Results: Institutes – Stepwise Regression
Stepwise regression / NMCR Step Status Coeff P-value
ECRj/ECRf = NMCR/RCR 1 In 1.5473 0
Average Number of Authors Out 0.3353
Expected Authors Rate Journal Out 0.3723
Expected Authors Rate Field 2 In 0.1326 0
Normalized Author Rate Journal Out 0.7983
Normalized Author Rate Field 4 In -0.0204 0
Average Number of Countries Out 0.7056
Expected Country Rate Journal 5 In -0.3697 0
Expected Country Rate Field Out 0.1624
Normalized Country Rate Journal 3 In 0.2764 0
Normalized Country Rate Field Out 0.4558

27. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Conclusions
The introduction of normalized collaboration
measures for both multi-authorship and
international collaboration helps us in
understanding the relation between collaboration
and citation scores by enhancing comparability
among fields
We observed strong correlations between averages
of authors and citations but when we take the
normalization into account the correlation does not
hold at all levels of aggregation

28. COLLNET 2011,
September 20-23,
Istanbul, Turkey
Conclusions
Countries: Only a correlation between
normalized citation scores and journal strategy is
observed.
Journals: By applying a field normalization all
correlations with field expected collaboration
scores dissapear. However, the correlation with
normalized collaboration scores remains.
Institutes: Here we see a more scattered image.