The following are normalized indicators:
- Category Normalized Citation Impact
- Journal Normalized Citation Impact
- Impact Relative to World
- Average Percentile
The Category Normalized Citation Impact (CNCI) of a document is calculated by dividing the actual count of citing items by the expected citation rate for documents with the same document type, year of publication and subject area. When a document is assigned to more than one subject area an average of the ratios of the actual to expected citations is used. The CNCI of a set of documents, for example the collected works of an individual, institution or country/region, is the average of the CNCI values for all the documents in the set.
For a single paper that is only assigned to one subject area, this can be represented as:
For a single paper assigned to multiple subjects, the CNCI can be represented as the average of the ratios for of actual to expected citations for each subject area:
For a group of papers, the CNCI value is the average of the values for each of the papers:
|e||Expected citation rate or baseline|
|p||Number of papers|
|f||The field or subject area|
|n||The number of subjects to which a paper is assigned|
|i||Entity being evaluated (institution, country/region, person, etc.)|
CNCI is a valuable and unbiased indicator of impact irrespective of age, subject focus, or document type. Therefore, it allows comparisons between entities of different sizes and different subject mixes.
- A CNCI value of 1 represents performance at par with world average.
- Values above 1 are considered above average.
- Values below 1 are considered below average.
- A CNCI value of 2 is considered twice world average.
A quirk of the way we calculate baselines (whole counting of subjects for papers in more than one subject category) and CNCI (fractional counting of subjects for papers in more than one subject category) result in the CNCI of the world not being equal to one exactly.
CNCI is an ideal indicator for benchmarking at all organizational levels (author, institution, region etc). You can also use CNCI to identify impactful sub-sets of documents and assess any research activity. For example, an institution may use the CNCI to assess which collaborations are most impactful or identify new potential collaboration opportunities. An institution may also use CNCI to identify the performance of up-and-coming researchers compared to established ones, and aid with faculty recruitment by assessing candidates. As a funding organization, you may use the CNCI as a quantitative performance indicator to monitor the performance of funded projects, or assess the track record of a research teams applying for new funding.
Known Issues Using CNCI
When dealing with small sets of publications, for example, the publications of one individual, the CNCI values may be inflated by a single highly cited paper.
Because CNCI is an average, when looking at larger sets of publications, such as the collected works of an institution, very highly cited papers can have a large influence on the CNCI value.
The baseline values for current year can be very low and therefore the CNCI values for current year can fluctuate more than expected.
Steps to Resolve CNCI Issues
- Use the CNCI value alongside other indicators to have a picture of performance as a whole and to identify anomalies and data artifacts.
- Use larger sets of publications when possible, for example, by extending the time period or expanding the number of subjects covered.
- Show care when analyzing documents from most recent publication years. Include documents from a range of years for more meaningful analysis.
- Limit your analysis to significant research publications to the document type of Article or Review. If appropriate, to aid increased coverage of some fields, consider document types Book Chapters and Conference Proceedings.
- Always use citation indicators to aid and not replace human judgment.
Complementary Indicators Useful with CNCI
- Journal Normalized Citation Impact
- % Documents in Top 1% and % Documents in Top 10%
- Average Percentile
The Journal Normalized Citation Impact (JNCI) indicator is a similar indicator to the Normalized Citation Impact, but instead of normalizing per subject area or field, it normalizes the citation rate for the journal in which the document is publishing.
The Journal Normalized Citation Impact of a single publication is the ratio of the actual number of citing items to the average citation rate of publications in the same journal in the same year and with the same document type. The JNCI for a set of publications is the average of the JNCI for each publication.
The JNCI indicator can reveal information about the performance of a publication (or a set of publications) in relation to how other researchers perform when they publish their work in a given journal (or a set of journals). It can provide the answers to questions, such as “How do my papers perform in the journals I publish?” If the numerical value of the JNCI exceeds one, then the assessed research entity is performing above average. If it is less than one, then it is performing below the average.
The JNCI indicator is also useful for publishers as a measure of post–publication performance and it can reveal which research work exceeds average performance and therefore increases the citation rates of a journal.
|Researcher||Total Publications||Total Citations||Citation Impact||H-index||Normalized Citation Impact||Journal Normalized Citation Impact|
This table shows an example of the application of the NCI and JNCI indicators at the author level. Researcher D and Researcher E both have similar numbers of publications and citations. Their Citation Impact is almost the same, and their h-index is identical. Using only the first four indicators featured in table 1, it is not possible to distinguish the performance of the two researchers. However, the two researchers may be conducting research in very different fields and may have a different history of publication (older papers vs new papers). Using the NCI and JNCI indicators gives us a better understanding of their performance relative to their peers in terms of subject, document type and age of publication.
From the normalized indicators, one can quickly identify that Researcher D has both NCI (1.32) and JNCI (1.86) values that are above average (>1).
While Researcher E has a NCI (0.45) and JNCI (0.72) that are below average (<1). Note that the JNCI is a relative research performance indicator. Even though in many cases NCI and JNCI might correlate positively, this might not always be the case. For example, if for a given researcher the NCI indicator is above average while at the same time the JNCI indicator is below average, this might mean that the researcher receives more citations than the average for their published research work in the scientific field that the researcher is active in overall, but they publish in journals with high citation rates (e.g., Nature or Science) and received less citations than the average published work does for the given journals.
Citation impact of the set of publications as a ratio of world average.
Apply this indicator at the institutional, national, and international level. It shows the impact of the research relative to the impact of the global research, and it's an indicator of relative research performance. The world average is always equal to one. If the numerical value of the Impact Relative to World exceeds one, then the assessed entity is performing above the world average. If it is less than one, then it is performing below the world average.
Although this indicator does normalize for year, it does not take into account the differences in the subject mix that an institution or a country/region is publishing in; therefore, it is recommend to use it in conjunction with bibliometric indicators that do take into account the differences in the average citation rates of the set of documents under evaluation.
The percentile of a publication is determined by creating a citation frequency distribution for all publications in the same year, subject category, and document type (arranging the papers in descending order of citation count), and determining the percentage of papers at each level of citation. If a paper has a percentile value of one, then 99% of the papers in the same subject category, year, and document type have a lower citation count.
A percentile is a normalized indicator because it indicates how a paper performed relative to others in its field, year, and document type. For any set of papers, an Average Percentile can be calculated as the harmonic mean of all the percentiles of all the papers in the set. In the case that a paper is assigned to more than one category, the category in which the percentile value is closest to 0 is used (the best performing value). Percentile values are rounded to the second decimal place.