Division of Dermatology, Department of Medicine, Roskilde Hospital, DK4000 Roskilde, Denmark
Abstract
Background
The impact factors of scientific journals are interesting but not unproblematic. It is speculated that the number of journals in which citations can be made correlates with the impact factors in any given speciality.
Methods
Using the Journal Citation Report (JCR) for 1997, a bibliometric analysis was made to assess the correlation between the number of journals available in different fields of clinical medicine and the top impact factor. A detailed study was made of dermatological journals listed in the JCR 1991–2000, to assess the relevance of this general survey.
Results
Using the 1997 JCR definitions of speciality journals, a significant linear correlation was found between the number of journals in a given field and the top impact factor of that field (rs = 0.612, p < 0.05).
Studying the trend for dermatological journals 1991 to 2000 a similar pattern was found. Significant correlations were also found between total number of journals and mean impact factor (rs = 0.793, p = 0.006), between the total number of journals and the top impact factor (rs = 0.759, p = 0.011) and between the mean and the top impact factor (rs = 0.827, p = 0.003).
Conclusions
The observations suggest that the number of journals available predict the top impact factor. For dermatology journals the top and the mean impact factor are predicted. This is in good agreement with theoretical expectations as more journals make more printspace available for more papers containing citations. It is suggested that new journals in dermatology should be encouraged, as this will most likely increase the impact factor of dermatological journals generally.
Introduction
Bibliometric analysis of scientific publications has become an independent area of research, and may with some reservations be used in the analysis of the output from scientifically active institutions and organisations
The impact factor is calculated by dividing the number of quotations a given journal receives by the number of papers published in a given period of time, and therefore equals the average number of times a paper in the journal is quoted. This may depend on the quality of the paper, but equally on many other factors. One prime factor of importance to specialist topics such as dermatology is the opportunity to quote a given paper. The more special a given topic is, the fewer opportunities exist for quoting it and hence the lower the impact factor.
Materials and methods
The study was conducted in two steps: a general and a specific dermatological. The ISI Journal Citation Report^{®} (JCR) was used in both. In order to study the general correlation between the number of journals in a given field (as defined by the JCR) and the top impact factor achieved was studied for 1997. In order to assess the relevance of this overall finding for dermatology a further study was conducted of the dermatological journals listed in the JCR for 1991–2000, correlating average impact factor, top impact factor, year and number of journals for all the journals listed in the 2000 edition.
Simple descriptive statistics were calculated for individual journals, and nonparametric statistics were used where appropriate. In the assessment of high or low impact and growth trends, low was defined as values below the 95% confidence interval of the mean. Conversely, high was defined as values above the 95% confidence interval of the mean. A value of p < 0.05 was considered significant.
Results
The results of the general survey are shown in Table
The figure shows a scatterplot of top journal impact factor in a given specialist field.
The figure shows a scatterplot of top journal impact factor in a given specialist field as a function of the total number of journals in that field as defined by JCR 1997.
The maximum impact factor and number of journals in different fields of medicine for 1997.
Field
Highest impact factor
No. Of journals
Biochemistry
40,782
253
Immunology
37,796
117
Cell biol.
37,297
130
Medicine (exp)
28,114
61
Medicine (gen)
27,766
100
Endocrinology
23,017
81
Microbiology
18,153
73
Oncology
11,403
102
Psychiatry
10,751
67
Gastoenterology
10,250
42
Cardiology
9,762
62
Haematology
9,762
59
Pathology
6,501
66
Rheumatology
6,167
18
Surgery
5,954
114
Ophthalmology
5,250
39
Anaesthetics
4,625
21
Dermatology
4,584
32
Allergology
3,797
18
Paediatrics
3,793
66
Bioch. Res. Methods
3,181
33
Mycology
2,442
15
Ortopaedics
2,242
37
ENT
1,915
26
For the period 1991 – 2000 the JCR has included an increasing number of dermatological journals. In 1991 only 27 journals were listed, while in 2000 a total of 36 dermatological journals were listed. In the same period the top impact factor has risen from 3.855 to 4.539, and the mean impact factor for dermatological journals from 1.018 to 1.247, but the difference between the years was not significant. A significant correlation was found between total number of journals and mean impact factor (rs = 0.793, p = 0.006), between the total number of journals and the top impact factor (rs = 0.759 (p = 0.011) and between the mean and the top impact factor (rs = 0.827, p = 0.003).
Using multiple regression to study the relationship between the mean impact factor of all the dermatological journals and yeartoyear variation and variation in the number of journals a significant relation was found (F = 68.993, p < 0.001). This was due to the number of journals (t = 3.324, p = 0.013) rather than to the yeartoyear variation (t = 1.082, not significant).
Summary data of trends in impact factor for the period 1991–2000 and the coefficient of variation of impact factors for dermatological journals, are presented in table
The trends in journal impact factor in dermatology.
Journal
Trend of impact factor 1991 – 2000
Coefficient of variation of impact factor 1991 – 2000
Acta dermatovenerologica
0,81632
0,267
Am J Dermpath
0,04796
0,152
Ann dermatol Vener
0,403771
0,205
Arch Dermatol
0,884012
0,218
Arch Dermatol Res
0,491905
0,112
Br J Dermatol
0,702629
0,099
Burns
0,896953
0,490
Clin Dermatol
0,896953
0,398
Clin Exp Dermatol
0,782753
0,09
Contact dermatitis
0,151598
0,162
Cutis
0,781086
0,281
Dermatol Clin
0,737733
0,414
Derm Surg/JDSO
0,788775
0,510
Dermatology
0,01982
0,160
Eur J Dermatol
0,55886
0,236
Exp Dermatol


Hautarzt
0,901278
0,229
Int J dermatol
0,932871
0,219
J Am Acad Dermatol
0,917437
0,164
J Cosm Sci
0,927102
0,578
J Cut Pathol
0,173582
0,177
J Derm Sci
0,904308
0,302
J Dermatol Treatm
0,453902
0,317
J Eur Acad Derm Venerol


J Invest Dermatol
0,810147
0,129
Leprosy Rev
0,40046
0,338
Melanom Res
0,389372
0,103
Mycoses
0,868254
0,288
Pediatr Dermatol
0,870963
0,375
Photodermatol Photo
0,755563
0,264
Semin Cut Med Surg
0,903769
0,263
Sex Transm Dis
0,537911
0,199
Sex Transm Inf
0,872954
1,144
Skin Pharmacol
0,408128
0,194
Wounds
0,13274
0,287
Mean
0,6330
0,247
95% confidence interval of mean
0,522 – 0,745
0,194–0,2995
Discussion
There appears to be a general correlation between the number of journals in a given field and the top impact factor achieved. This is in good agreement with logical expectation, i.e. more journals publishing papers on a given topic make more printspace available for more papers containing specific citations. Large specialist areas or general areas of medical science will therefore achieve higher impact factors in purely bibliometric studies
Looking specifically at dermatology a similar pattern appears. A larger number of indexed journals correlate significantly with a higher mean and top impact factor. Multiple regression analysis suggests that the number of journals is of greater importance than yeartoyear fluctuations in impact factor.
Looking at trends for impact factors over the decade differences appear between journals, with some journals having a highly positive trend, e.g. Int J Dermatol, while others have a negative tenyear trend, e.g. Wounds. The coefficient of variation (=SD/mean) for each journal's impact factor has also been calculated as a measure of the stability of the trends. Differences appear to suggest low, average or high variation of impact factor over time. By combining trend and variation it becomes possible to identify different patterns of development, see Table
Different development trends for dermatological journals.
Above average trend (high growth)
Average trend
Below average trend (low growth)
Above average COV (volatile)
Burns, Clin Dermatol, Derm Surg/JDSO, J Cosm Sci, J Derm Sci, Pediatric Dermatol, Sex Transm Inf,
Dermatol Clin,
J Dermatol Treatm, Leprosy Rev,
Average COV
Acta dermatovernerologica, Arch Dermatol, Hautarzt, Int J Dermatol, Mycoses, Photodermatol Photo, Semin Cut Med Surg,
Sex Transm Dis
Ann Dermato Venerol, Arch Derm Res, Skin Pharmacol, Wounds
Below average COV (stable)
Clin Exp Dermatol, Cutis, J Am Acad Dermatol, J Invest Dermatol,
Br J Dermatol
Am J Dermpath, Contact dermatitis, Dermatology, J Cut Pathol, Melanoma Res,
Conclusions
Specialist topics require specialist journals. If the dermatological society wishes to increase the journal the top and mean impact factor of its journals, one option appears to be to encourage the inclusion of new journals in the relevant indexes, thereby offering authors opportunity for publishing and quoting. It is unlikely that the available publishing space will ever match the ingenuity of the human mind, and a continuous publishing pressure will therefore continue to exist. Some of the published ideas will inevitably be better than other, but nearly all publications will contain citations and hence influence the impact factors of journals.
Competing interests
None declared
Prepublication history
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