Nanyang Technological University

​Citations and Research Impact

1. Measuring Research Impact
2. Research Impact of Researchers
3. Research Impact of Journals

1. Measuring Research Impact

Publication and citation counts are increasingly used to measure the impact of scholarly research. Institutions and government agencies are using metrics related to publication and citation numbers to evaluate and rank research output and research impact of researchers, research institutes and even of a country.

While it is good to have some way to measure research performance and evaluate your research, it is also important to note the following:

  • Measuring research impact through citation counts is just ONE quantitative indicator
    There are other quantitative and qualitative approaches to measuring research and they should be used collectively to obtain a holistic view of the research and its impact. Citation counts and related citation metrics is just ONE quantitative indicator of research performance.

  • Citation patterns differ between subject disciplines
    Citation metrics should not be compared across disciplines as citation patterns differ between subject disciplines.

  • Citation databases are not complete
    The different citation databases cover different journals and in totality, they do not cover the world’s entire scientific and scholarly output. There are many publications not captured in these citation databases. Hence, the results from the citation databases are not comprehensive and should not be compared.


2. Research Impact of Researchers

Here are some metrics used to measure the research impact of researchers:

  • Number of publications
    This refers to the total number of publications a researcher has published in the researcher’s lifetime or within a defined period of time (e.g. last five years).
    This number is often used as an indicator of the researcher’s productivity.

  • Number of citations received from publications
    This refers to the total number of times a researcher’s work has been cited by other research publications. The publications can be based on the entire collection of published work by a researcher or the publications within a defined period (e.g. last five years). This number is often used as an indicator to measure the quality of research. The assumption is that the greater the impact of the research, the more citation it will receive.

  • h-index
    h-index is a number used to measure the productivity and influence of a researcher.
    Definition of h-index: a researcher with an index of h has published h papers, each of which has been cited at least h times.
    (i.e. A researcher with an index of 5 has published 5 papers, each of which has been cited at least 5 times.)


3. Research Impact of Journals

Here are some metrics you can use to rank the journals by measuring the impact of these journals:

  • Journal Impact Factor
    The Impact Factor (IF) of a journal is the average number of times articles from the journal published in the past two years have been cited in the Journal Citation Report* Year.


    i.e. If Journal A has an impact factor of 5, on average, the articles published in Journal A within the last 2 years have been cited 5 times.


    Hence, publications in journals with higher IF may have higher chances of being cited as compared to publications published in journals with relatively lower IF.

    Researchers often use IF to help them decide where they should publish their research.
    It is important to note that IF measures the impact of a journal and does not measure the researchers publishing in the journal. Institutions often use IF as an indication to evaluate their researchers on the assumption that papers published in these journals of high IF are of higher quality and have higher chances of being cited.

  • 5-year Impact Factor
    The 5-year IF is the average number of times articles from a journal published in the last five years have been cited in the JCR year (as compared to the last 2 years for IF).


    The 5-year IF may be more appropriate for subject disciplines where it may take longer than two years to disseminate and respond to published works (e.g. Arts and Humanities). The 5-year IF is also good for the researchers to see how citation patterns of the journal changes over a longer period of time.

  • Cited half-life
    This refers to the median age of the articles that were cited in the JCR year.
    E.g. The Cited Half-Life of Journal A in 2011 is 7.4. This means that it takes 7.4 years for the papers published in Journal A in the year 2011 to reach 50% of their total lifetime citations.
    The Cited-Half Life shows if the journal has a good track record and shows how long content in the journal is still being referred to after publication.

  • Immediacy Index
    Immediacy Index refers to the number of times a paper published in a year is cited within that same year.
    E.g. Immediacy Index of Journal A is 2.24. This means that the papers Journal A published in the year 2011 were cited, on average, 2.24 times in 2011.


*Journal Citation Report (JCR) is available via Web of Knowledge. JCR lets you search across the Science or Social Sciences Edition to obtain journal information based on citation data. More details here.

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