Are there really two types of h index variants A validation study by using molecular life sciences d

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Are there really two types of h index variants? A
validation study by using molecular life sciences
data

• Lutz Bornmann, Rüdiger Mutz, Hans-Dieter Daniel,
  Gerlind Wallon, Anna Ledin

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h index

• h index as a criterion to quantify the scientific
  output of a single researcher
• A scientist has index h if h of his or her Np
  papers have at least h citations each and the
  other (Np - h) papers have h citations each
  (Hirsch, 2005, p. 16569)

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Advantages of the h index

• It gives a robust estimate of the broad impact of
  a scientists cumulative research contributions
• It combines number of publications and citation
  counts in a balanced way

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Disadvantages of the h index

• It is only weakly sensitive to the number of
  citations received by single publications
• It is highly dependent upon a scientists number
  of years of active research
• It can only rise and cannot decline
• Some new Hirsch-type indices have been proposed

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Definitions of the h index and its variants
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Statistical analysis

• Intercorrelational structure using factor
  analysis
• The factor analysis provides information on the
  dimensionality of the structure of the
  dependencies in a data set
• We examined whether the indices are based on a
  single factor (such as a research performance
  dimension) or whether there are several factors
  involved

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The data set for the investigation of the indices

• Committee peer review for awarding long-term
  fellowships to post-doctoral researchers as
  practiced by the Boehringer Ingelheim Fonds
  (B.I.F., www.bifonds.de)
• 414 post-doctoral applicants (64 approved and 350
  rejected) from the years 1990 to 1995
• 1,586 papers published previous to applying for
  the fellowship (publication window 1986 - 1994)
• The papers received a total of 60,882 citations
  (according to the Science Citation Index)
  (citation window from year of publication to the
  end of 2001)

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Box plots of the nine logarithmic indices
calculated for the B.I.F. applicants with the
distribution of data and the Gaussian bell curve
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Varimax rotated loading matrix of a ML factor
analysis for nine log transformed indices (n414)
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Varimax rotated loading matrix of a ML factor
analysis for 11 log transformed indices or
standard bibliometric measures (n414)
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First conclusions

• There are two types of indices/ measures
• The one type of indices/ measures (for example h
  index and g index) describe the most productive
  core of the output of a scientist and tell us the
  number of papers in the core
• The other indices/ measures (for example a index
  and m index) depict the impact of the papers in
  the core
• There is an empirical incremental contribution
  with the variants that depict the impact of the
  papers in the productive core

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Paper

• Bornmann, L., Mutz, R., Daniel, H.-D. (2008).
  Are there better indices for evaluation purposes
  than the h index? A comparison of nine different
  variants of the h index using data from
  biomedicine. Journal of the American Society for
  Information Science and Technology, 59(5),
  830-837

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The data set for the validation of the two-factor
solution

• 693 applicants to the Long-Term Fellowship
  programme of the European Molecular Biology
  Organization (EMBO, http//www.embo.org/) from
  the year 1998
• The programme has gained an excellent reputation
• 3,351 papers (articles, letters, notes, and
  reviews) published prior to application(publicati
  on window 1993 1998)
• The papers received an average of 45 citations
  (according to the Science Citation Index)
  (citation window from year of publication until
  2006)

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Statistical analysis

• Two further indices hm index and maxprod.
• Eleven indices were included in the factor
  analysis
• ML Factor Analysis
• Logarithmized index values

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Varimax rotated loading matrix of a ML factor
analysis for eleven log transformed indices
(n693)
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Varimax rotated loading matrix of a ML factor
analysis for 13 log transformed indices or
standard bibliometric measures (n693)
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Second conclusions

• There are two types of indices
• Both index types can complement each other very
  well
• An empirical incremental contribution associated
  with the variants that depict the impact of the
  papers in the productive core
• We propose the use of any pair of indices as a
  meaningful indicator for comparing scientists
  one index relates to the number and the other to
  the impact of the papers in the productive core