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Introduction
Scientific journals
play an important role in managing and distributing of
knowledge in the scientific information community; therefore
it is crucial to be aware about the role of journals in the
knowledge community.
There are some
important indicators for evaluating the journals capacities;
among them the Impact Factor has got its place as a general
evaluation factor. Journals IF depends directly on two
elements:
-
The citations that the journal receive in the fiscal year.
-
The articles that published in the 2 previous years.
Although the Impact
Factor should be used cautious, “I expected that it
would be used constructively while recognizing that in the
wrong hands it might be abused.”
But on the whole it is a feasible measurement in the hand of
bibliometricians and librarians.
Such indicators make
it possible to judge relatively fair about the importance of a
journal among other journals in the same field. It may help
the librarians and the administrators of libraries in decision
to choose journals for their patrons use in the libraries as
well as to register the electronic journals to facilitate
their patrons’ access
to
information retrieval more effectively and attractively via
remote access.
In spit of some
authors’ eager tendency in the interdisciplinary fields to
publish their works in the journals with high IFs, to get
higher prestige among their colleagues at institutes due the
reason that their work published in the journals with high IF
may receives more citations; There are still many authors in
different fields, that they don’t have enough information
about the IF.
“The Impact Factor
was devised by Eugene Garfield, the founder of the Institute
for Scientific Information, now part of Thomson, a large
worldwide US-based publisher. Impact factors are calculated
each year by the Institute for Scientific Information for
those journals which it indexes, and the factors and indices
are published in Journal Citation Reports. Some related
values, also calculated and published by the same
organization, are:
-
The immediacy index: the average citation number of an
article in that year
-
The journal cited half-life: the median age of the articles
that were cited in Journal Citation Reports each year. For
example, if the A journal's half-life in 2005 is 5, that
means the citations from 2001-2005 are 50% of all the
citations from that journal in 2005.
-
The aggregate impact factor for a subject category: it is
calculated taking into account the number of citations to
all journals in the subject category and the number of
articles from all the journals in the subject category.”
With an example the
calculation of the IF seems easier.
For example the
German journal of Endoscopy in 2005 has an IF equalled to
4.072.
It is calculated as
the following formula:
Number of article
published in 2003= 152 (A)
Number of article
published in 2004= 138 (B)
Number of cites in
2005 to articles published in 2003= 661 (C)
Number of cites in
2005 to article published in 2004= 520 (D)
IF=
Analysis of data
showed that there is a correlation between total-citation and
IFs of journals, 32.9% of all total-citation in the JCR in
2005 belong to the 7% of journals with IF > 3, and 67.1% of
total-citation belong to 93% of journals with IF< 3.
The study showed
that 91% of all German journals indexed in the JCR in 2000 has
self-citation rate from 1% to 79%, and 96% of all population
in 2005 has self-citation rate from 1% to 72%.
From a total of 427
German journals indexed in the JCR in 2005, 89% of all
population are published in English or multi-language, and
only 11% is published in German-language.
Method and
Materials
All journal
self-citation and impact factor data focused on this study
were chosen from the Journal Citation report of ISI web of
knowledge available at
http://portal.isiknowledge.com/portal.cgi?DestApp=JCR&Func=Frame.
The self-citation rate specified as the percentage of the
journal self-citation from total citation of the journal in
the year of under study. For example the journal of “NEUROPSYCHIATRIE”
in 2005 was cited 100 times. Of this 100 times, 72 times cited
by itself.
As a result the
self-citation rate is: =
= 0.72
In order to compare
the German journals characters with all journals indexed in
the JCR, the whole journals indexed in the JCR was divided
into 3 groups:
1.
High
rank journals, the journals with IF higher than 9.846.
2.
Middle
rank journals, the journals with IF between 4.352 and 5.
3.
Low
rank journals, the journals with IF lower than 0.052.
the reason of
choosing the journals with IF higher than 9.846 as the first
group is that after sorting all journals in the JCR in 2005,
the first 100 journals IFs levelled higher than 9.846, and the
last 100 journals IFs levelled lower than 0.052. In
consequence the second group stayed in the JCR between two
other groups.
To show the trend of
IFs for German journals, the Impact Factor of all German
journals indexed in the JCR throughout 2000-2005 were
extracted, and the mean value of IFs was calculated.
Findings
Table1: The portion
of German journals entering material in the JCR database in
2005
|
All journals
in the JCR |
German
journals in the JCR |
|
Year |
No. of journals |
Articles |
Citations |
No. of journals |
Articles |
Citations |
|
2005 |
6,088 |
847,114 |
22,353,992 |
427 |
7% |
50,276 |
6% |
861,190 |
4% |
As the table
indicates, the portion of German journals entering material to
the JCR database in 2005 counted 4%. From a total number of
6088 journals in the JCR, 427 (7%) were published in Germany.
The 6088 journals in the JCR produced 847,114 articles, 50,276
(6%) appeared in the German journals. Of the 22,353,992
citations in 2005, 861,190 (4%) came from German journals.
Fig.1: The growth of
journals IFs (mean value) for all German journals indexed in
the JCR 2000-2005
The graph shows a
lineal correlation between the mean values of German journals
IFs and the year of publication.
Fig.2 Impact Factor
versus total-citation in 427 German journals in 2005
Fig.3: Impact Factor
versus self-citation in 345 German journals in 2005
Table 2:
self-citation rate of German journals in 2000
|
Self-citation rate |
No. of journals |
Percent |
|
0- 5% |
97 |
22.40 |
|
5-10% |
121 |
27.94 |
|
10-15% |
68 |
15.70 |
|
15-20% |
62 |
14.32 |
|
20-25% |
36 |
8.31 |
|
25-30% |
23 |
5.31 |
|
30-35% |
6 |
1.39 |
|
35-40% |
9 |
2.08 |
|
40-45% |
7 |
1.62 |
|
45-50% |
0 |
0.00 |
|
>50% |
4 |
0.92 |
|
Total |
433 |
100.00 |
As the table
indicates 77.60% of all German journals in 2000 have
self-citation rate at or more than 5%, and 19.63% of all
population has self-citation rate more than 20%
Table 3:
self-citation rate of German journals in 2005
|
Self-citation rate |
No. of
journals |
Percent |
|
0- 5% |
100 |
23.4 |
|
5-10% |
134 |
31.38 |
|
10-15% |
74 |
17.33 |
|
15-20% |
53 |
12.41 |
|
20-25% |
23 |
5.39 |
|
25-30% |
19 |
4.45 |
|
30-35% |
6 |
1.41 |
|
35-40% |
6 |
1.41 |
|
40-45% |
5 |
1.17 |
|
45-50% |
2 |
0.47 |
|
>50% |
5 |
1.17 |
|
Total |
427 |
100.00 |
As the table shows
from a total number of 427 German journals indexed in the JCR
in 2005, 76.58% of them has at or more than 5% citation to
their own and 15.46% of total population has self-citation
rate more than 20%.
Table 4: the mean
value of self-citation rate and IF of all German journals
indexed in the JCR (2000 and 2005)
|
Year |
No. of journals |
Mean value of
self-citation rate |
Mean value of IF |
|
2000 |
433 |
12% |
0.98 |
|
2005 |
427 |
12% |
1,29 |
The mean value of
self-citation rate in 2000 as well as in 2005 is 12% of all
citations. The mean value of all journals IFs in 2005 with
compare to the 2000 has 0.31 increased.
Table 5: the mean value of
360 German journals IFs in 2000 and the same set of journals
in 2005.
|
Year |
No. of
journals |
Mean value
of self-citation rate |
Mean value
of IF |
|
2000 |
360 |
13% |
1.02 |
|
2005 |
360 |
11% |
1,29 |
As the table
illustrates the mean value of IF for German journals in 2005
with compare to the same set of journals in 2000 has 0.27
increased. The self-citation rate of German journals in 2005
shows 2% decrease with compare to the same set of journals in
2000.
Fig. 4: German
journals based on self-citation rank 2000
As the graph shows
the journal of ZKG INTERNATIONAL with 79% of self-citation
rate get the first rank, followed by WOCHENBLATT FUR
PAPIERFABRIKATION and EUROPEAN JOURNAL OF LIPID SCIENCE AND
TECHNOLOGY with 68% and 63% of self-citation rate
respectively.
The table restricted to the
eleven high self-citation rank journals (self-citation rate >
40%).
Fig. 5: German journals based
on the self-citation rank in 2005
As the graph shows
the journal of NEUROPSYCHIATRIE with 72% of
self-citation rate get the first rank followed by
The comparison of
self-citation rate in 2000 and the same set of journals in
2005 (360 journals) showed that the self-citation rate of 32%
of all journal has increased and the self-citation rate of 61%
of all of them decreased and the self-citation rate of 7%
stayed unchanged.
Fig6: Difference of
360 German journals Impact Factors in 2005 with the same set
of journals in 2000 in the JCR
As the graph
illustrates 70.83% of German journals IF indexed in the JCR
shows positive growth in 2005 with compare the same set of
journal in 2000. The journal of “Review of Physiology
Biochemistry and Pharmacology” shows dramatic increase in the
term of IF, its IF increased from 5.389 in 2000 to 17.053 in
2005, and the journal of “European Physical Journal C” shows
dramatic decrease throughout the period of study its IF
decreased from 5.408 in 2000 to 3.209 in 2005.
Fig. 7: Comparison
of total-citation and self-citation for 360 German journals in
2000 and the same set of journals in 2005 indexed in the JCR.
As the graph shows
the number of total citation as well as self-citation for the
German journals in 2005 with compare to the same set of
journal in 2000 has increased. Total citation in 2005 shows
26.67% growth in compare to the same set of journals in the
year 2000, and self-citation shows 22.45% growth.
Fig.8: Comparison of
total citation and self-citation for all German journals
indexed in the JCR 2000-2005.
As the graph shows,
the number of total citation in 2005 shows 19.93% increase
with compare to the all German journals citation in 2000.The
number of self-citation for all German journals in 2005 shows
13.55% increase with compare to the self-citation of journals
in 2000.
Fig. 9 self-citation
versus IF (Pearson’s correlation = 0, 57)
Fig. 10
self-citation rate versus IF (Pearson r = 0.22)
Table 6: Mean value
of journals self-citation rate for 3 groups of journals in the
JCR 2005
|
IF |
No. of
selected journals |
Percent of
selected journals in the JCR |
Mean
value of self-citation rate |
No. of
total-citations |
No. of
self-citations |
Mean value
of total-citation per journal |
Mean value
of self-citation per journal |
|
IF > 9.846 |
100 |
1.64% |
2% |
3,255,988 |
75,497 |
32,559.88 |
754.97 |
|
4.352< IF > 5 |
100 |
1.64% |
6% |
1,085,570 |
101,486 |
10855.70 |
1014.86 |
|
IF < 0.052 |
100 |
1.64% |
17% |
10,613 |
1,999 |
106.13 |
19.99 |
From all 6,088
number of journals indexed in the JCR in 2005 ascent sorted
based on the IF, a total number of 100 journals with highest
IF (IF>9.847), 100 journals with middle IF (4.352< IF > 5),
and 100 journals with lowest IF (IF<0.052) were chosen in
order to compare the total-citation and self-citation
behaviours in the JCR.
As the Table
indicates, the mean value of self-citation rate among journals
with highest IF is 2% and this rate among the journals with
lowest IF is 17%, in other words the self-citation rate among
the journals with lowest IFs in the JCR is more than 8 times
higher than the self-citation rate of journals with highest
IFs.
Although the
self-citation rate among the journals with highest IFs is 8.5
times lower than the self-citation rate among the journals
with lowest IFs, but it should be noticed that mean value of
total citation per journal among journals with highest IFs is
307 time higher than the mean value of total-citation per
journal among the journal with lowest IFs. And the mean value
of self-citation per journals among the first group (the
journals with highest IFs) is 38 times higher than the later
group (the journals with lowest IFs). Therefore it is
remarkable to be noticed when it is discussed about the
self-citation rate among the journals with high IFs and as
well as with low IFs.
Table 7 the mean
value of citations rate for all German journals in the JCR
2005
|
Impact
Factor |
No. of German journals
In the JCR |
Percent
|
Mean
value of self-citation rate |
| | 