Table 2.

Overview of Commonly Used Bibliometrics (Adapted6)

MetricDefinition(s)Comments
PublicationsNumber in peer-reviewed journalsSome publications may be missed because authors do not include grant number in their manuscripts
Number of original research articles (ie, excluding reviews, commentaries, and editorials)Incentives for “salami slicing”
Number in high-impact journalsSome consider focus on journal impact (as assessed by impact factor) to be a “mortal sin”
Along with citations, can be used to measure the extent and impact of scientific teamwork
Difficult to assess the relative contributions of multiple coauthors
Difficult to assess the relative contributions of specific grants and contracts for publications that credit multiple grants and contracts
Difficult to compare across fields
CitationsTotal numberHighly correlated with scientific field, career stage, personal reputation
Number in peer-reviewed journalsMay spread misinformation, reflecting network phenomena rather than genuine scientific impact14
Number per publicationMay not necessarily reflect positive impact on field
Number weighted for impact factor of citing journal
Number weighted for number of coauthors
Number weighted for scientific field
Impact FactorFor a journal, the impact factor for year y is the number of citations appearing in year y to articles published in years y-1 and y-2, divided by the total number of “citable articles” published in years y-1 and y-2Not a valid measure of individual researchers or an individual article
Even for high-impact journals, most citations come from a small proportion of articles
Difficult to compare across fields
H-indexFor a researcher (or laboratory, department, or any unit), the h-index is the number of publications that have been cited at least h times (eg, an h-index of 40 means a researcher has published at least 40 articles that have each been cited at least 40 times)Measures the impact of a large body of work
Correlates with other measures of scientific recognition, like Nobel prizes
Can only increase with age, meaning it is unable to detect declining impact
Difficult to compare across fields
Online accessesNumber of visitsAssesses impact beyond other scientists who publish articles
Number of downloadsStandards not yet developed