Vallmitjana.indd

Citation Analysis of Ph.D.
Dissertation References as a Tool
for Collection Management in an
Academic Chemistry Library

Núria Vallmitjana and L. G. Sabaté

A bibliometric study was carried out on the citations within the chemis-
try field Ph.D. dissertations to ascertain what types of documents are
the most frequently used in the research process, the most frequently
consulted journals and obsolescence rate of the journals. The analysis
covered 46 doctoral theses presented at the Institut Químic de Sarriá
(IQS) from 1995 to 2003. The results obtained from the 4,203 citations
revealed that the most frequently used documents were scientific papers,
which accounted for 79 percent of the total; 33 journals met 50 percent
of the informational needs; and the age of 50 percent of the citations was
no older than 9 years. Finally, the results can be used as a tool for the
collection management of the library.

About the IQS Introduction
The Institut Químic de Sarriá (IQS) of the It seems paradoxical that, in the informa-
Universitat Ramon Llull is an academic tion age, it could be so difficult to have
centre founded by the “Compañía de all the journals published in a specific
Jesús” in 1905 and located in Barcelona, scientific field available. Some of the main
Spain. In the last hundred years, teaching reasons are: the great number of scientific
and research in Chemistry and Chemical journals published, their high subscrip-
Engineering has been its main interest. tion cost, with yearly price increases that
Its Chemical Engineering course has are significantly higher than the standard
been ABET-accredited since September of living increase, and the budgetary
2004. Its Ph.D. courses in Chemistry restraints of academic libraries. These
and Chemical Engineering received the reasons force the libraries to establish
Quality Mention from Spanish Govern- priorities in their collection acquisitions
ment in 2003. and maintenance policy in accordance

Núria Vallmitjana is associated with the Library at the Institut Químic de Sarriá (Universitat Ramon Llull);
e-mail: nuria.vallmitjana@iqs.edu. L. G. Sabaté works in the Department of Applied Statistics, Facultat
d’Economia IQS (Universitat Ramon Llull); e-mail: lgsab@iqs.edu. The authors would like to thank the
students of the 2001–2005 Business Administration and Management at the IQS for analyzing most of the
theses as part of a joint practical work for both “Information Management” and “Statistics” courses. Our
thanks also go to Martí G. Gatell, who developed the database that was used in this educational activity,
and X. Tomás for his useful comments.

mailto:lgsab@iqs.edu
mailto:nuria.vallmitjana@iqs.edu

Citation Analysis of Ph.D. Dissertation References as a Tool 73

with the users’ needs. The users’ needs
can be identified by the analysis of the
scientific literature usage of students,
teachers, and researchers.1

Journal usage can be estimated by the
number of citations contained in the docu-
ments published by researchers as the
articles in scientific journals, conference
papers or postgraduate dissertations.
These documents contain a great num-
ber of bibliographical citations because
“students tend to be exhaustive and
chronologically complete in the review
of the literature.”2

The analysis of the Ph.D. dissertation
citations constitutes a good method for
the evaluation of journal usage, because it
is the best way of identifying the sources
of information looked up by the research-
ers and, therefore, justifies the investment
devoted to the subscriptions.3

This work studies the bibliographical
references of the Ph.D. dissertations in
Chemistry, as a source of information to
manage the scientific journal collection
in the academic library. The analysis an-
swers the following questions:

• What is the proportion of journals
cited?

• What are the most cited journals?
• Is there any relationship between

the top journals’ rank and their impact
factor?

• How old are the cited articles?
• How much is the cost per cita-

tion?
The results can be used as management

criteria for the literature collection of a
library. The results let us decide about re-
newals, subscriptions, and cancellations of
the journals. It will also help us to manage
the situation of the journals in the avail-
able space by their obsolescence rate.

The revision of the literature we
present shows that there are few works
published in this field and all have been
carried out in libraries of the United
States, and this is the first and only work
that refers to a European centre.

The bibliometric analysis carried out
in this study uses a methodology similar

to the one used by Chrzastowski4 in 1991
and by Gooden5 ten years later. Both
works are centered on Chemistry and
come from data obtained in a local-use
study. Nevertheless, the first study uses
four parameters (the reshelving of all
journals picked up throughout the library
each day, use through in-house circula-
tion, journal lending and borrowing, and
through interlibrary loan). On the other
hand, the second study uses the citations
of the Ph.D. dissertations as a frequency
indicator of journal use.

Literature Review
The analysis of the citations cited in the
Ph.D. dissertations has been the tool to
evaluate the researchers’ information
needs and the role of libraries to satisfy
those needs. Kushkowski6 organizes in a
table some of the most important works
published in the last years in different ar-
eas of knowledge. In all of the works there
is an increase of citations as time goes by,
although the number of citations changes
in each discipline, and it is recommended
to study monographically this trend in
each of these areas.

The bibliometric study of Buchanan
and Herubel7 in Political Science con-
cludes that scientific journals represent
the biggest proportion of materials cited
in the dissertations and that the materials
cited in these documents and the analysis
of them allow the library a be er manage-
ment of the collection.

Sylvia and Lesher8 apply the method
of analysis of citations from theses and
dissertations to the field of Psychology.
Their study evaluates two parameters
that are complementary: the number of
journals that are most frequently cited
and their cost-per-use.

Zipp9 not only analyzes the citations of
the dissertations to evaluate the collection
of the library specialized in Geology, but
also studies the citations of the articles
published by the researchers and com-
pares both results.

Bu lar10 analyses the citations of Ph.D.
dissertations on Library Science and

74 College & Research Libraries January 2008

Information Science for the evaluation
of the nature of material cited most, the
authors, the countries of origin of pub-
lications cited, the journals cited, their
range of topics and how current is the
literature cited.

Smith11 studies the results of the cita-
tions analysis of a sample of theses from
2001 about several different topics and
compares them with the analysis realized
ten years before. He evaluates the useful-
ness of the library collection and investi-
gates its evolution through time, in accor-
dance with the introduction of electronic
information sources and with the massive
increase in the cost of subscriptions to
scientific journals. Arts and Humanities
tend to depend more on monographs;
meanwhile, Science and Technology use
mostly scientific journals. The age of the
cited materials also establishes several
differences: Science and Technology seem
not to be interested in old material like
Arts and Humanities.

Haycock12 analyzes the citations in dis-
sertations on Education Sciences, finished
between 2000 and 2002 to establish which
are the journals that were most frequently
used as well as the relationship between
monographs and articles of scientific
journals.

Gooden13 analyzes the Ph.D. disserta-
tions of the Ohio State University Chem-
istry Department between 1996 and 2000.
The conclusion reached is that only 12
journals are necessary to cover 50 percent
of the references and demonstrates that
most of the citations correspond to articles
published in scientific journals.

Another work in the Chemistry field
is one of Chrzastowski14 that also studies
the use of journals in the library of the
University of Illinois at Urbana-Cham-
paign (UIUC). She calculates the cost-ef-
fectiveness of the collection to establish
which subscriptions should be cancelled
considering that the relationship price/
use is too high. In comparison with the
aforementioned works, the use of the
collection is measured with four indica-
tors (the reshelving count of all journals

picked up throughout the library each
day, the number of issues used through
in-house circulation, the lending and bor-
rowing journal count and also through
interlibrary loan). In this work, the journal
usage is not measured by means of the
citations contained in the Ph.D. disserta-
tions. Chrzastowski and Olesko15 con-
tinue with the former study and analyze
the trends of use and cost of the journals
in the UIUC Chemistry Library.

Methodology
The starting material for this work is the
front page of each thesis and the literature
cited.

The information registered for each
thesis is:

• identification data, including the
year;

• the number of documents cited:
monographs, theses and academic disser-
tations, articles, and other documents;

• for each cited article there is an
identification code (theses-article), the
journal title and the publication year.

Data has been processed in the fol-
lowing way:

• citation analysis according to docu-
ment type;

• bibliometric analysis of the cited
journals: frequency distribution and im-
pact factor;

• description of the citation age dis-
tribution;

• cost per citation study.

Results
From 1995 to 2003, 68 Ph.D. theses were
presented in the Institut Químic de
Sarrià (IQS), in Chemistry or Chemical
Engineering fields. Twenty-two theses
were put aside because they presented
the bibliography in chapters or because
they were not available. The results ob-
tained from the 46 theses analyzed are
as follows:

What is the Proportion of Journals Cited?
According to the document type, 79 per-
cent are articles in scientific journals, 12

Citation Analysis of Ph.D. Dissertation References as a Tool 75

percent are monographs, and 2 percent
are theses or academic dissertations.

Citations numbering 4,203 are articles
published in 593 journals. The relation-
ship between the number of cited articles
and the number of cited journals is 7.1.
The average number of scientific articles
cited per theses is 91.

What are the Most Cited Journals?
In accordance with Bradford’s16 Law, most
of the articles on a certain subject are pub-
lished in a reduced number of journals.
The analysis of the studied references
reveals that a core formed by 33 journals
satisfies 50 percent of the informational
needs and that 150 journals are needed
to reach 80 percent of the informational
necessities as shown in Figure 1.

Table 1 lists the 33 journal titles needed
to satisfy 50 percent of the journal cita-
tions in this study.

From the 33 titles that constitute
the core journals, 14 belong to Organic
Chemistry and Biochemistry, 9 to Gen-
eral Chemistry; meanwhile, the rest are
distributed in several areas such as Envi-
ronmental Science, Electrochemistry, and
Corrosion among others.

Taking into account the publisher of
this core journal, 58 percent of titles come
from three publishing firms:

• 9 belong to Elsevier (27%);
• 6 belong to the American Chemical

Society (18%);
• 4 belong to Wiley-VCH (12%).
For the rest of the journals, 12 have

been published by different scientific
societies and only 2 belong to commercial
publishing firms (Nature Publishing and
Thieme).

Is There Any Relationship Between the Top
Journals’ Rank and Their Impact Factor?
The impact factor for 2003 of the top jour-
nals obtained from Journal Citation Reports
varies from 0.157 to 30.979. Figure 2 shows
that there exists a moderate association be-
tween the position of a core journal and its
impact factor rank measured with the cor-
relation coefficient of Spearman (rs=0.5194;
p-value=0.0033). This possible association
must be studied more in-depth.

How Old are the Cited Articles?
The reference age is defined as the time
passed between the publication year of an
article and the thesis reading year where
this paper is cited. Figure 3 shows the
frequency distribution of citation ages.
The mean is 14 years with a median of 9
years, while 90 percent of citations are 31
years old or fewer; however, the range is
145 years.

FIGURE 1
Citations Accumulated According to the Number of Journals

that Included Them

Bradford's Law

0
10
20
30
40
50
60
70
80
90
100

0 50 100 150 200 250 300 350 400 450 500 550 600

Number of journals

%
c
it
a
ti
o
n
s

(
a
c
c
u
m
)

650

76 College & Research Libraries January 2008

TABLE 1
Top 33 Core Journals Cited

Rank
Core
Journal

Citations
(%)

Accum.
Citations
(%)

Journal Title Impact
Factor
2003

Rank
Impact
Factor
2003

Cost per
Citation
(€)

1 6.87 6.87 Journal of the American
Chemical Society

6.516 4 0.20

2 5.28 12.15 Journal of Organic
Chemistry

3.297 9 0.18

3 4.60 16.75 Tetrahedron Letters 2.326 15 1.09
4 2.52 19.27 Tetrahedron 2.641 12 2.27
5 2.03 21.30 Angewandte Chemie.

International Edition in
English

8.427 3 0.85

6 1.78 23.08 Chemosphere 1.904 22 1.08
7 1.47 24.55 Biochemistry 3.922 7 1.05
8 1.43 25.98 Journal of Medicinal

Chemistry
4.820 5 0.55

9 1.36 27.34 Journal of the
Electrochemical
Society

2.361 13 0.26

10 1.31 28.65 Afinidad 0.157 31 0.01
11 1.26 29.91 Tetrahedron:

Asymmetry
2.178 16 0.90

12 1.24 31.15 Environmental Science
& Technology

3.592 8 0.51

13 1.21 32.36 Helvetica Chimica Acta 1.861 23 0.69
14 1.21 33.57 Journal of Biological

Chemistry
2.361 14 0.71

15 1.14 34.71 Carbohydrate Research 1.533 26 2.71
16 1.12 35.83 Nature 30.979 1 0.60
17 1.07 36.90 Chemical Reviews 21.036 2 0.38
18 1.07 37.97 Journal of

Chromatography
2.922 11 5.22

19 0.96 38.93 Journal Chemical
Society. Perkin
Transactions I

1.948 21 ———

20 0.93 39.86 Syntheses 2.074 18 0.62
21 0.91 40.77 Biotechnology and

Bioengineering
2.173 17 2.31

22 0.91 41.68 Electrochimica Acta 1.996 20 2.10
23 0.91 42.59 Heterocycles 1.082 29 2.02

Citation Analysis of Ph.D. Dissertation References as a Tool 77

TABLE 1
Top 33 Core Journals Cited

Rank
Core
Journal

Citations
(%)

0.91

Accum.
Citations
(%)

43.50

Journal Title

Journal Chemical
Society

Impact
Factor
2003

——

Rank
Impact
Factor
2003

Cost per
Citation
(€)

——

25 0.91 44.41 Journal Chemical
Society. Chemical
Communications

4.031 6 0.80

26 0.86 45.27 Chemistry Letters 1.579 24 0.20
27 0.84 46.11 Chemical Engineering

Science
1.562 25 2.66

28 0.84 46.95 Corrosion 0.774 30 0.17
29 0.77 47.72 Journal of

Organometallic
Chemistry

2.042 19 6.21

30 0.75 48.47 Bulletin of the
Chemical Society of
Japan

1.237 27 0.45

31 0.75 49.22 Chemische Berichte —— 33 ——
32 0.75 49.97 Journal of Chemical

Physics
2.950 10 3.47

33 0.65 50.62 Canadian Journal of
Chemistry

1.157 28 0.68

How Much is the Cost Per Citation?
The last aspect considered is the economic
cost of the core journals. If we take the
subscription cost for 2004, the library must
have spent about 100,000 € to maintain the
subscriptions of the core journals.

At the same time, considering the 46
theses studied, the subscription price of
the core journals and the number of cita-
tions for each journal, the average cost is
about 1 € / citation; 57 percent of the jour-
nals have a cost lower than 1.00 €/citation;
meanwhile, 14 percent have a cost higher
than 3.00 €/citation (see table 1).

Discussion
As highlighted in table 2, the results ob-
tained in this work (Vallmitjana column)
are comparable to the ones of other works
cited before.

All the works included in the table
were published by different authors
between the years of 1994 and 2004.
The methodology used is based on
the bibliometric analysis of the ref-
e r e n c e s c o n t a i n e d w i t h i n d o c t o r a l
theses from different universities in
the United States. Most of the studies
are centered in the thesis of an specific
subject except for the multidisciplinary
studies of Kushkowski and Smith.17
The chronological timeframe is also
variable; some studies cover Ph.D. dis-
sertations from a specific year, whereas
other ones cover theses from several
years. The proportion of references
analyzed also varies; in some cases, all
the references are analyzed, whereas
in others only a representative sample
is studied.

http:Smith.17

Frequency Distribution of Citation Ages

78 College & Research Libraries

In the mentioned works,
one can conclude that the
number of references con-
tained within doctoral theses
increases with time; the au-
thors a ribute this to the fact
that information is more and
more easily accessible. Also,
they conclude that the average
number of references by thesis
varies between subjects. So-
cial Sciences and Arts and Hu-
manities use fewer references
than those of Natural Sciences
(Kushkowski, Smith18). These
facts are reflected in the com-
parison of results in table 2.
The work of Gooden,19 in the
field of Chemistry, states that
86 percent of references were
scientific papers published
in journals. Kushkowski 2 0
indicates that the percentage
of journals used in Biology and Physics
also surpassed 80 percent. For Smith,21
in the field of Sciences, the percentage
was also 80 percent; Arts and Humani-
ties are those that use 20 percent fewer
journals, whereas the percentage in
Social Sciences is situated between 40
and 60 percent.

January 2008

FIGURE 2

Relationship Between the Core Journals’

Rank and their Impact Factor Rank

Relationship between ranks
40

Im
p
a
c
t
F
a
c
to
r
R
a
n
k

0
0 5 10 15 20 25 30 35 40

Core Journal Rank

Since only the work of Gooden22 is in
the area of Chemistry, we compared in
table 3 some relevant results of her work
and ours.

It is important to mention that the
number of journals needed to cover 50
percent of journal citations is very dif-
ferent between the Gooden study and
our study. Gooden establishes a group

FIGURE 3

Distribution of citation ages
350

300

250

200

n
150

100

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Age (years)

Citation Analysis of Ph.D. Dissertation References as a Tool 79

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of 12 titles; meanwhile, in our study the
core journals is composed of 33 titles.
Gooden determined that 20 titles included
61 percent of the journal references,
whereas in our study the 20 most used
titles cover only 40 percent of the journal
references.

Comparing the titles of the core jour-
nals of both studies, it has been observed
that:

• 8 titles appear in both lists: Journal
of the American Chemical Society, Journal
of Chemical Physics, Tetrahedron Letters,
Biochemistry, Journal of Organic Chemistry,
Journal of Biological Chemistry, Nature, and
Journal of the Chemical Society.

• Journal of the American Chemical
Society is the most cited in both cases
and has been cited 11.45 percent in the
Gooden’s study and 6.87 percent in the
present study.

With regard to the age of the cited
documents, the mean age was 14 years
with a median value of 9; meanwhile,
in the multidisciplinary study of Kush-
kowski,23 the mean was 12 years and the
median value 8.

Citation costs obtained in this study
are not comparable with the ones of
Chrzastowski and Olesko,24 because of
the differences in the methodologies
employed.

On average, 91 papers are cited in
each thesis, the cost per thesis amounts
to approximately 90 €. In contrast, if all
articles had been acquired through one
of the main document suppliers, this
would represent a cost of nearly 1,200 €
per thesis.

Conclusions
A bibliometric study was designed in ac-
cordance with scientific literature to study
the information needs of Ph.D. students.

A total of 4,203 citations in 593 journals
were analysed. The analysis accounted
for approximately 79 percent of the total
citations that were made in 46 of the 68
Ph.D. dissertations accepted by the IQS
(Institut Químic de Sarrià, Universitat
Ramon Llull) from 1995 to 2003.

80 College & Research Libraries January 2008

TABLE 3
Comparison of Results

Results Gooden Vallmitjana
(this paper)

Journals 86% 79%
Type of document Monographs 8% 12%

Theses 6% 2%
Total journal citations (A) 3,178 4,203
Number of different journals (B) 441 593
Ratio A/B 7.2 7.1
Number of Theses (C) 30 46
Mean = A/C 106 91
Number of journals needed to cover 50% of journal citations 12 33
Percentage of the journal citations covered by the first 20 61% 40%
titles (Note: we use 20 titles to compare with Gooden’s paper)

From the analysis, we conclude that:
• Scientific journals are the most

frequently used document type in IQS
chemistry Ph.D. dissertations. On aver-
age, 91 articles were cited in each thesis.

• 50 percent of the citations come from
33 core journals, which is less than 6 percent
of the total number of journals cited.

• A large proportion of the most cited
journals come from a small set of publish-
ing companies. Nearly 60 percent of the
core journals belong to 3 publishers.

• There is some evidence of a rela-
tionship between the impact factor rank
and the rank of the journal in terms of
citation frequency. This possible relation
must be studied more in-depth.

• The age of 50 percent of the citations
is no higher than 9 years, although the
mean age is 14 years.

No library has unlimited resources al-
lowing it to subscribe to all the journals
that their users request. Therefore, the
library must draw up an acquisitions
policy that concurs with the real pos-
sibilities and priorities in research areas.

We propose three criteria that a library
may use in deciding which subscriptions
to cancel and which to keep. The criteria
concludes the following:

• In agreement with the titles rank-
ing, core journals must have priority
because they are the most cited.

• The citation cost indicator will let
us establish a second level of priorities.
Subscriptions with a lower cost-per-cita-
tion may have preference to maximize the
resources assigned to journal acquisition.

• A reduced number of companies
publish a high number of journals. Gath-
ering the titles per publisher is a means
of assessing the financial viability of sub-
scribing to individual titles or packages,
in either printed or electronic format.

Last, having already developed an
analysis model, we can continue moni-
toring the situation merely by updat-
ing the data contained in forthcoming
Ph.D. theses. Discovering trends in how
specific academic journals are used can
help the library to get the most out of
its budget.

Notes

1. J. Thomson and R. Carr, An Introduction to University Library Administration (London:
Bingley, 1987).

Citation Analysis of Ph.D. Dissertation References as a Tool 81

2. C.A. Barry, “Information Skills for an Electronic World: Training Doctoral Research Stu-
dents,” Journal of Information Science 23, no. 3 (1997): 225–38.

3. T.E. Chrzastowski, “Journal Collection Cost-Effectiveness in an Academic Library: Results
of a Cost/Use Survey at the University of Illinois at Urbana-Champaign,” Collection Management
14, no. 1/2 (1991): 85–98.

4. Ibid.
5. A.M. Gooden, “Citation Analysis of Chemistry Doctoral Dissertations: An Ohio State

University Case Study,” Issues in Science and Technology Librarianship no. 32 (Fall) (2001).
6. J.D. Kushkowski, K.A. Parsons, and W.H. Wiese, “Master’s and Doctoral Theses Citations:

Analysis and Trands of a Longitudinal Study,” Libraries and the Academy 3, no. 3 (2003): 459–79.
7. A.L. Buchanan and J.P.V.M. Herubel, “Profiling Phd Dissertation Bibliographies: Serials

and Collection Development in Political-Science,” Behavioral & Social Sciences Librarian 13, no. 1
(1994): 1–10.

8. M. Sylvia and M. Lesher, “What Journals Do Psychology Graduate-Students Need: A
Citation Analysis of Theses References,” College & Research Libraries 56, no. 4 (1995): 313–18.

9. L.S. Zipp, “Theses and Dissertation Citations As Indicators of Faculty Research Use of
University Library Journal Collections,” Library Resources & Technical Services 40, no. 4 (1996):
335–42.

10. L. Bu lar, “Information Sources in Library and Information Science Doctoral Research,”
Library & Information Science Research 21, no. 2 (1999): 227–45.

11. E.T. Smith, “Assessing Collection Usefulness: An Investigation of Library Ownership of
the Resources Graduate Students Use,” College & Research Libraries 64, no. 5 (2003): 344–55.

12. L.A. Haycock, “Citation Analysis of Education Dissertations for Collection Development,”
Library Resources & Technical Services 48, no. 2 (2004): 102–06.

13. Gooden, “Citation Analysis.”
14. T.E. Chrzastowski and B.M. Olesko, “Chemistry Journal Use and Cost: Results of a Lon-

gitudinal Study,” Library Resources & Technical Services 41, no. 2 (1997): 101–11.
15. Ibid.
16. B.C. Brookes, “Bradford’s Law and the Bibliography of Science,” Nature 22 (2006): 953–

56.
17. Kushkowski et al., “Master’s and Doctoral Theses Citations”; Smith, “Assessing Collection

Usefulness.”
18. Kushkowski et al., “Master’s and Doctoral Theses Citations”; Smith, “Assessing Collection

Usefulness.”
19. Gooden, “Citation Analysis.”
20. Kushkowski et al., “Master’s and Doctoral Theses Citations.”
21. Smith, “Assessing Collection Usefulness.”
22. Gooden, “Citation Analysis.”
23. Kushkowski et al., “Master’s and Doctoral Theses Citations.’
24. Chrzastowski and Olesko, “Chemistry Journal Use and Cost.”