Impact Metrics - Impact Metrics and Scholarly Attribution

Author's H-Index

The Author's H-Index measures an individual researcher's productivity and impact.

Originally proposed in 2005, the H-Index has become the most popular measure of productivity and impact of individual researchers.
H-Index is based on a balance between the number of publications and the number of citations per publication.
An author with an H-index of X has published X papers that have each received at least X citations each.
H-Index is dependent on the length of a researcher's career. All else being equal, a researcher with a longer career is likely to have an H-Index because she has had more time to publish articles and accumulate citations.
H-Index measures sustained impact over time, and corrects for highly cited outliers. For example, an author with 100 citations to only 1 paper will have an H-Index of 1, while an author with 100 citations spread evenly between 10 papers will have an H-Index of 10.
Hirsch JE. An index to quantify an individual's scientific research output. Proceedings of the National Academy of Sciences of the USA. 2005;102:16569–16572. doi: 10.1073/pnas.0507655102. [PMC free article] [PubMed]

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Journal Impact Factor (Web of Knowledge)

The Journal Impact Factor (JIF) measures the average research impact of articles in individual journals.

JIF measures the average number of citations an article in a particular journal receives; shorter time intervals measure immediacy of impact while longer time intervals show sustained impact on future research. Annual JIFs can also be combined to form a longitudinal analysis of journal impact.
JIF scores vary significantly between research fields. For example, journals in internal medicine typically give and receive more citations than do journals in mathematics. Additionally, journals featuring a high proportion of review or methodological articles are likely to have higher JIF scores, regardless of journal quality or repuation.
The accuracy of JIF and other citation metrics depends entirely on the accuracy of indexed citations. Web of Science manually indexes citations exclusively from their Web of Science database. Automated citation indexes such as Microsoft Academic Search and Google Scholar often include duplicate citations, missing publications, and inclusion of citations from non-scholarly sources.
The JIF should not be used to measure the productivity of the researchers published in that journal, since individual researcher's work may be cited significantly more or less than the average that is measured by the JIF.
Garfield E. The history and meaning of the journal impact factor. JAMA. 2006;295:90–93. [PubMed]

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EigenFactor Score

The Journal EigenFactor Score (EF Score) measures the weighted research impact of individual journals.

EF Scores assigns greater weight to citations received from highly cited journals. EF Scores also correct for interdisciplinary differences in citation practices.
EF Scores are scaled such that the sum of all EF Scores equals 100. Thus, EF Scores can be interpreted as a percentage of total research impact.
A journal's EF score is a measure of the journal's total impact within the scientific community. With all else equal, a journal's Eigenfactor score doubles when the journal doubles in size. Thus, a very large journal such will have extremely high EF Score simply based upon its size.
EigenFACTOR methods and publications

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EigenFactor Article Influence Score

The EigenFactor Article Influence Score (AIS) measures the average impact of the articles in a journal over the first five years after publication.

Article Influence scores are normalized so that the mean article has an AIS of 1.00. This allows for absolute comparison of AIS scores to the average, and against other journals. For example, a journal with an AIS of 27 means that the average article in that journal has a research impact 27 times greater than the average article in the research literature.
EigenFACTOR methods and publications

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