Field normalized citation metrics are used to attempt to contextualize the citation rate of an article to the expected citation rate of other articles of the same field, publication type, and publication year.
Field normalized citation metrics are an article level metric.
The calculation of field normalized citation metrics depends on the type of metric you're using. Two common field normalized citation metrics types include the Relative Citation Ratio (RCR) from iCite and Field Weighted Citation Impact from Scopus.
Calculating the Relative Citation Ratio (RCR)
The RCR is calculated by taking an article's average annual citation rate (excluding the first calendar year in which the article was published) and dividing it by the expected citation rate of articles in the same co-citation network that were published in the same year. An RCR of 1 is considered average, while an RCR greater than 1 is above average.
Example: An article published in 2017 has been cited 5 times in 2017, 10 times in 2018, 5 times in 2019, and 12 times in 2020. The expected citation rate of articles in its co-citation network published in the same year is 6 citations per year.
To calculate the RCR, we first need to determine the average annual citation rate for the article (citations / years). The article's average annual citation rate would be (10 + 5 + 12) / 3 = 9 citations per year. Note that we are excluding citations from 2017, as RCRs exclude the first calendar year in which the article was published. So the RCR would be 9 citations per year / 6 citations per year = 1.5
This would mean that the article is being cited an average of 50% more times per year than expected for articles within its co-citation network published in the same year.
Note: RCRs are only available for articles in PubMed. RCRs will also only take into account citations from articles in PubMed (i.e., citations from publications that are not in PubMed will not be factored into an article's RCR). Additionally, articles less than 2 years old with less than 5 citations will not have an RCR (e.g., an article published in 2021 will not receive an RCR in 2022 unless it has 5 or more citations).
For additional information on how RCRs are calculated, see Hutchins et al.'s (2016) paper.
Calculating Field Weighted Citation Impact (FWCI)
Field weighted citation impact (FWCI) is calculated by dividing the total number of citations an article has received the year it was published and 3 complete calendar years after its publication by the average number of citations articles of the same field, publication type, and publication year are expected to receive within the same time period. A FWCI of 1 is considered average, while a FWCI of greater than 1 is above average.
Example: An article published in October 2017 has been cited 8 times in 2017, 5 times in 2018, 5 times in 2019, 5 times in 2020, and 15 times in 2021. The expected number of citations articles of the same field, publication type, and publication year have received within the same time period is 18.
We first need to add up the number of citations the article has received the year it was published and the 3 calendar years following its publication (i.e., 2017 to the end of December, 2020). So we would take 8 + 5 + 5 + 5 = 23 citations. Note we are excluding the number of citations received in 2021, as FWCIs only include citations to an article 3 complete calendar years after its publication. So the FWCI would be 23 / 18 = 1.28
This would mean that the article was cited 28% more times than expected for articles of the same field, publication type, and publication year.
Note: FWCIs in Scopus will only take into account citations from articles indexed in Scopus (i.e., citations from publications that are not indexed in Scopus will not be factored into an article's FWCI in Scopus).
For additional information on how FWCI is calculated, see the Snowball Metrics Recipe Book (page 55).
How to read an RCR:
How to read an FWCI:
Finding an article's RCR in iCite
Finding an article's FWCI in Scopus
Like any metric, field normalized citation metrics have their limitations. Some of these limitations include:
For a high-level overview of normalized metrics and their limitations, see:
For an overview of the RCR and how it's calculated, see:
Hutchins BI, Yuan X, Anderson JM, Santangelo GM. Relative Citation Ratio (RCR): A new metric that uses citation rates to measure influence at the article level. PLoS Biol. 2016;14(9):e1002541. Published 2016 Sep 6. doi:10.1371/journal.pbio.1002541.
For an overview of FWCIs and how they're calculated, see:
For a quick overview of field weighted citation impact metrics (which includes FWCI), see: