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What do we know aboutthe h index?  <br />Patricia Weiss, MLIS  Health Sciences Library System<br />University of Pittsbur...
Today’s article<br />Bornmann L, Daniel HD. What do we know about the h index? J Am Soc Inf Sci Technol. 2007;58(9):1381-1...
What is the h Index?<br />Proposed by Hirsch (2005)<br />Quantifies scientific output of a single researcher as a single n...
h index and the Scientific Life Cycle<br />A scientist's h index never decreases<br />It increases as…<br />New high-impac...
Advantages of h<br />Estimates broad impact of cumulative research contributions (Hirsch, 2005)<br />Insensitive to citati...
Article #71 in results list<br />Cited by 72 articles<br /> h=71<br />
Article #87 in results list<br />Cited by 87 articles<br /> h=87<br />
Cited by 111 articles<br /> h=111<br />Article #111 in results list<br />
Applications of the h Index<br />Micro vs. meso level applications<br />Micro: single researcher<br />Meso (intermediate):...
Convergent Validity of the h Index<br />Hirsch computed h indices for:<br />Nobel Prize physicists in the last 20 years<br...
Correlates that Establish Convergent Validity<br /><ul><li>Bornmann and Daniel (2006)
Peer review committee for Boehringer Ingelheim Fonds postdoctoral fellowships
Average h indices of approved applicants higher than those of rejected applicants
Cronin and Meho (2006)
Rankings of influential US information scientists
Strong positive correlation between h and raw citation counts</li></li></ul><li>Convergent Validity Correlates (2)<br /><u...
Looked at correlations between h and other bibliometric indicators
h and other bibliometrics: both relate comparably to peer judgments
Kelly and Jennions (2006)
Looked at publication output of 187 editorial board members (ecologists and evolutionary biologists) of 7 journals
Closely correlated with h</li></li></ul><li>Convergent Validity Correlates (3)<br /><ul><li>Lehmann, Jackson, and Lautrup ...
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What do we know about the h index?

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Bornmann L, Daniel HD. What do we know about the h index? J Am Soc Inf Sci Technol. 2007;58(9):1381-1385.

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What do we know about the h index?

  1. 1. What do we know aboutthe h index? <br />Patricia Weiss, MLIS  Health Sciences Library System<br />University of Pittsburgh<br />© 2009-2010 Patricia M. Weiss<br />
  2. 2. Today’s article<br />Bornmann L, Daniel HD. What do we know about the h index? J Am Soc Inf Sci Technol. 2007;58(9):1381-1385.<br />Review of research inspired by:<br />Hirsch JE. An index to quantify an individual’s scientific research output. Proc Natl Acad Sci U S A 2005;102(46):16569-16572.<br />Also will allude to:<br />Bornmann L, Daniel HD. The state of h index research. EMBO Rep 2009;10(1):2-6.<br />
  3. 3. What is the h Index?<br />Proposed by Hirsch (2005)<br />Quantifies scientific output of a single researcher as a single number:<br />An h index of 40 means that a scientist has published 40 papers that each had at least 40 citations.<br />“… original and simple new measure incorporating both quantity and visibility of publications”<br />
  4. 4. h index and the Scientific Life Cycle<br />A scientist's h index never decreases<br />It increases as…<br />New high-impact papers are published<br />Sleeping Beauties come to life (van Raan, 2004)<br />A scientist's papers attract citations <br />
  5. 5. Advantages of h<br />Estimates broad impact of cumulative research contributions (Hirsch, 2005)<br />Insensitive to citation extremes<br />Infrequently cited or noncited papers<br />“One-hit wonders”<br />It “favors enduring performers that publish a continuous stream of papers with lasting and above-average impact.”<br />
  6. 6. Article #71 in results list<br />Cited by 72 articles<br /> h=71<br />
  7. 7.
  8. 8. Article #87 in results list<br />Cited by 87 articles<br /> h=87<br />
  9. 9. Cited by 111 articles<br /> h=111<br />Article #111 in results list<br />
  10. 10. Applications of the h Index<br />Micro vs. meso level applications<br />Micro: single researcher<br />Meso (intermediate): group of researchers<br />Scientific facilities<br />Countries (Csajbók et al, 2007)<br />h - b index based on topic or compound search in Web of Science (Banks, 2006) <br />How much work has already been done on topic?<br />What topic is hot or mainstream now?<br />
  11. 11. Convergent Validity of the h Index<br />Hirsch computed h indices for:<br />Nobel Prize physicists in the last 20 years<br />Physicists and astronomers elected to National Academy of Sciences in 2005<br />Highly cited scientists in biological and biomedical sciences<br />Hirsch’s threshold values<br />Successful scientist: h=20 after 20 years<br />Outstanding scientist: h=40 after 20 years<br />Truly unique individual: h=60 after 20 years, or 90 after 30 years<br />
  12. 12. Correlates that Establish Convergent Validity<br /><ul><li>Bornmann and Daniel (2006)
  13. 13. Peer review committee for Boehringer Ingelheim Fonds postdoctoral fellowships
  14. 14. Average h indices of approved applicants higher than those of rejected applicants
  15. 15. Cronin and Meho (2006)
  16. 16. Rankings of influential US information scientists
  17. 17. Strong positive correlation between h and raw citation counts</li></li></ul><li>Convergent Validity Correlates (2)<br /><ul><li>van Raan (2006): 147 Dutch university chemistry research groups (700 researchers, 18K publications)
  18. 18. Looked at correlations between h and other bibliometric indicators
  19. 19. h and other bibliometrics: both relate comparably to peer judgments
  20. 20. Kelly and Jennions (2006)
  21. 21. Looked at publication output of 187 editorial board members (ecologists and evolutionary biologists) of 7 journals
  22. 22. Closely correlated with h</li></li></ul><li>Convergent Validity Correlates (3)<br /><ul><li>Lehmann, Jackson, and Lautrup (2005)
  23. 23. Used papers from high-energy physics database
  24. 24. Presented method for quantifying reliability of one-dimensional measures based on citation and publication data
  25. 25. Mean, median, maximum citations were reliable measures of scientific performances
  26. 26. h was not (lacks accuracy and precision)</li></li></ul><li>Disadvantages of WoS-Derived h<br />Publication and citation may actually be lower if multiple authors of same name<br />Or, may be higher (Roediger, 2006)<br />Only journals selected by Thomson Scientific are indexed<br />Unclear citations (e.g., “in press”)<br />Incorrect citations (e.g., wrong first page number)<br />Only journal articles are counted<br />(Also, noted in WoS documentation: subscription depth as factor)<br />
  27. 27. Journal Impact Factors in Tenure and Promotion<br />
  28. 28. Potato, Potahto<br />Simplistic<br />BUTmeasures broad impact of one's work<br />Can’t differentiate between active and inactive scientists<br />BUT never decreases<br />Can’t differentiate between no longer significant works and those now shaping scientific thinking<br />BUTalso can't spotlight works which are "trendy”--this is a bad thing?<br />
  29. 29. Different disciplines, different citation patterns: should be used to compare only scientists of similar professional age working in similar disciplines<br />BUTHirsch himself noted that h in biosciences higher than in physics<br />Combining publication and citation frequencies into one value "posits an equality between two quantities with no evident logical connection"<br />BUT preferable to other single-number criteria (total number of papers; total number of citations; citations per paper)<br />
  30. 30. "Think of two scientists, each with 10 papers with 10 citations, but one with an additional 90 papers with 9 citations each; or suppose one has exactly 10 papers of 10 citations and the other exactly 10 papers of 100 each. Would anyone think them equivalent?”<br />BUT2 individuals with similar hs are comparable in terms of their overall scientific impact, even if their total number of papers or their total number of citations is very different.<br />
  31. 31. Indices that Correct or Complement h<br />One that corrects for self-citations*<br />m quotient: Corrects for bias toward researchers with longer careers/more papers*<br />Ones that look at a definite time period, such as c (for most recent calendar year)<br />hI: Normalizes for different numbers of co-authors in different fields*<br />a and g indexes: More sensitive to highly cited papers—the scientist’s “top performers”<br />* Proposed or developed by Hirsch himself<br />
  32. 32. Conclusion<br />No thorough validation of the h index yet in its various applications<br />Would need to entail… <br />Cross-discipline validation <br />Broad statistical data<br />So, h index and its derivatives and alternatives “should not (yet) be used as a criterion to inform decision making in science…”<br />
  33. 33. What do we know aboutthe h index? <br />Pat Weiss  HSLS Journal Club  March 4, 2009<br />

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