Impact Factors: how to get one, how to improve it, how to understand it.

Elaine Stott(Journal Publishing Director, Blackwell Publishing)

ISAJE Annual Meeting 2nd September 2006

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Impact Factor

• Eugene Garfield created The Science Citation Index (SCI) in 1961 as a quarterly printed index, - 600 journals.

• Aim to look at relationships between researchers – who was citing who?

• Journal Impact Factor was used for journal selection.

• Never intended to be used as it is today – librarians, grants, RAE in UK, authors

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The Impact Factor

Cita

tions

Time after publication (Years)0 2 4 8 106 18161412 20

The average number of citations the average article receives per annum in the 2 years after publication

Article published in Jan 2003 will have longer to contribute cites to 2005 IF than an article published in Dec 2004

e.g. the 2005 impact factor will be the total citations in 2005 to articles published in 2003 and 2004 / no. articles published in 2003 and 2004

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Document Type

Letters: Rapidly climbs to citation peak, large proportion of cites in 2 year window – but low absolute number

Full Papers: Later citation peak, smaller proportion in 2 year window, but greater longevityReviews: Latest citation peak of three document types, and greatest longevity. Proportion of cites within impact window is low - but high absolute number of cites

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Variation in Impact Factors (Mabe & Amin, 2000)

Significant variation in mean impact according to subject areaTop journal in one field may have a lower impact than bottom journal in another field.

Significant effect of multiple authorshipCan be field specific.

Comparisons should only be made within the same subject areas

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Impact Factor Fluctuation: Size of Journal

Correlation between impact factor fluctuation and size of journalA journal of 200 papers per year might expect up to ± 15 % fluctuationFor an impact of 1.5 this would mean a range of 1.27 -1.72 implies no significant change

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Cita

tions

Time after publication (Years)

0 2 4 8 106 18161412 20

The Immediacy Index

No. of citations in the current year / No. articles published in that year

A measure of skewness of the citation curvei.e. how quickly are the articles being cited?

Some evidence that the II appears to be correlated with IF, i.e. a change in II is followed by a change in IF – useful early warning signal.

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Cita

tions

Time after publication (Years)

0 2 4 8 106 18161412 20

The Cited Half-Life

The number of years that the total citations (i.e. citations to articles from all years, rather than only the previous two years) takes to decline to 50% of its value

A measure of rate of decline of the citation curvei.e. article longevity

50% of citations

50% of citations

No evidence that the cited half-life is correlated with IF

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Getting an Impact Factor

• Today covers 8,500 of a total of 20-30,000 journals (c. 35% of all journals).

• ISI aim to include most internationally influential journals in each subject area

• 2,000 journals evaluated every year -both new +already included jnls

• 150-200 new added each year

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Getting an Impact Factor

• ISI aim to include most internationally influential journals in each subject area

• 2,000 journals evaluated every year -both new +already included jnls

• 150-200 new added each year

Details on ISI website:

http://scientific.thomson.com/mjl/selection/#jsc

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Selection criteria for inclusion in ISI database

• Basic Journal Publishing Standardsa. Timeliness of Publication?

b. International Editorial Conventions?

c. English Language Bibliographic Information?

d. Peer Review?

• Editorial coverage – does the journal add anything new, how does it compare to other journals waiting to be added?

• International diversity ( take International + best national Journals)?

• Number of citations

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Analysis of citations

• Related journals

• Top cited institutions

• Top cited authors

• Where are top cited papers being published

• Which subjects are getting most citations

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Addiction journals

Addiction journals are listed in Journal Citation Reports:

ScienceSubstance abuse – ( 8 journals) IF range 0.9 -3.6Psychiatry (84 Journals) IF range 0.05 -12.6Pharmacology and Pharmacy (193 Journals) IF range 0.1 -

19.83Toxicology (75 Journals) IF range 0.2-19.3Psychology (60 Journals) IF range 0.1 - 9.7

Social ScienceSubstance abuse – (18 Journals) IF range 0.5 - 3.6Psychology, general – (111 Journal) IF range 0.02 - 9.7Psychology, clinical (53 Journals) IF range 0.05 -5.0Social Issues (31 Journals) IF range 0.7 -1.6

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2005 Impact factors – Science -substance abuse

1 ADDICTION 3.696

2 DRUG ALCOHOL DEPEN 2.969

3 ALCOHOL CLIN EXP RES 2.636

4 ALCOHOL ALCOHOLISM 2.04

5 ADDICT BIOL 1.846

6 ALCOHOL 1.743

7 J STUD ALCOHOL 1.654

8 SUBST USE MISUSE 0.983

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2005 Impact factors – Social Science -substance abuse

1 ADDICTION 3.696

2 PSYCHOL ADDICT BEHAV 2.098

3 J SUBST ABUSE TREAT 2.077

4 EUR ADDICT RES 1.667

5 J STUD ALCOHOL 1.654

6 DRUG ALCOHOL REV 1.618

7 ADDICT BEHAV 1.581

8 AM J ADDICTION 1.47

9 ALCOHOL RES HEALTH 1.179

10 AM J DRUG ALCOHOL AB 1.094

11 SUBST USE MISUSE 0.983

12 J ADDICT DIS 0.894

13 J DRUG ISSUES 0.812

14 J PSYCHOACTIVE DRUGS 0.752

15 J DRUG EDUC 0.741

16 DRUG-EDUC PREV POLIC 0.619

17 ADDICT RES THEORY 0.594

18 J CHILD ADOLES SUBST 0.579

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Analysis of citations

• Related journals

• Top cited institutions

• Top cited authors

• Where are top cited papers being published

• Which subjects are getting most citations

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Papers 2002-2006 in impact factor journals

Finland  Total articles

98Total citations

256

  Addiction 30 63

 Alcohol &

Alcoholism 29 78

  ACER 19 65

 

Substance Use & Misuse 7 1

  DAD 4 27

  Alcohol 3 11

  Addiction Biol 3 4

  J. Sub. Abuse 3 7