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 NIH-funded 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.

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.

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:

• For example, Article A has an RCR of 1.2. This means that Article A is cited an average of 20% more times per year than expected for articles within its co-citation network published in the same year.

How to read an FWCI:

• For example, Article B has an FWCI of 1.4. This means that Article B is cited an average of 40% more times than expected for articles of the same field, publication type, and publication year.

You can find an article's field normalized citation metrics in either iCite or Scopus.

Finding an article's RCR in iCite

1. Go to iCite
2. Enter the title of the article into the search bar
3. Scroll to the bottom of the page and click "Process"
4. Scroll down until you see a table
5. The RCR will display on the right-hand side of the table

Finding an article's FWCI in Scopus

1. Go to Scopus
2. Enter the title of the article into the search bar
3. Look for the article in your results list
4. Click the article's title to go to its metadata page
5. Scroll down until you see the "Metrics" heading
6. Click to carrot next to the "Metrics" heading
7. The FWCI shoudl display on the right (labeled "Field weighted citation impact")

Like any metric, field normalized citation metrics have their limitations. Some of these limitations include:

• Field categorizations and their granularity differ between sources
• Document type categorizations and their granularity differ between sources
• May be skewed by cross-disciplinary citations
• Expected citation rates may be skewed by outliers
• Citation counts (which are used to inform the metric) differ between databases
• Citation counts (which are used to inform the metric) do not exclude self citations
• Not all citations (which are used to inform the metric) are "good" citations (e.g., Article A may cite Article B to reject Article B's findings)
• Does not take into account social impact (e.g., an article trending on Twitter)
• Like all impact metrics, vulnerable to gamification (e.g., citation rings)

For a high-level overview of normalized metrics and their limitations, see:

• Ioannidis JP, Boyack K, Wouters PF. Citation metrics: A primer on how (not) to normalize. PLoS Biol. 2016;14(9):e1002542. Published 2016 Sep 6. doi:10.1371/journal.pbio.1002542.

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.

• Relative citation ratio. Metrics Toolkit. https://www.metrics-toolkit.org/metrics/relative_citation_ratio/

For an overview of FWCIs and how they're calculated, see:

• Snowball Metrics Recipe Book: Their application in the United Kingdom. Snowball Metrics, eVision, Inc.; 2012.

For a quick overview of field weighted citation impact metrics (which includes FWCI), see:

• Field weighted citation impact. Metrics Toolkit. Accessed April 8, 2022. https://www.metrics-toolkit.org/metrics/field_weighted_citation_impact/