Understanding the impact indicators of scientific publications

In the field of biomedical research and health sciences, the reputation and influence of a scientific journal are often assessed using bibliometric indicators. These impact factors measure the visibility and citation frequency of articles published in a journal, and help researchers choose where to publish or which sources to prioritise.

Here is a comprehensive overview of the main impact indices used today.

1. Impact Factor (IF)

The impact factor is the best-known bibliometric indicator. Calculated annually by Clarivate Analytics in the Journal Citation Reports (JCR), it measures the average number of citations received in one year by articles published in the journal during the previous two years.

Formula:
Number of citations in year N of articles published in N-1 and N-2 / Number of articles published in N-1 and N-2

Example:
If a journal published 100 articles in 2022 and 2023, and in 2024 these articles were cited 400 times, its impact factor will be 4.

Limitation:
The impact factor varies significantly across disciplines. It is therefore not very relevant to compare journals from different fields based on this metric alone.

2. CiteScore

CiteScore, offered by Elsevier through Scopus, is based on a similar principle but covers a four-year period and includes a broader range of document types (articles, letters, editorials, etc.).

Formula:
Number of citations in year N of documents published from N-1 to N-4 / Number of documents published from N-1 to N-4

Advantage:
CiteScore is freely accessible and updated more frequently than the impact factor.

3. SNIP (Source Normalized Impact per Paper)

SNIP is an indicator that adjusts the number of citations according to citation habits specific to each scientific field.

Particularity:
A field where articles are on average less cited (e.g., mathematics) is thus fairly compared to a more citation-rich field (such as medicine).

4. SJR (SCImago Journal Rank)

SJR assigns a weighted score to journals by considering not only the number of citations but also the importance of the journals from which the citations come.

Principle:
A citation from a highly influential journal carries more weight than a citation from a marginal journal.

Source:
The ranking is freely available on the SCImago Journal & Country Rank platform, based on Scopus data.

5. Quartiles: Positioning a Journal within Its Field

In addition to these numerical indices, journals are classified into quartiles within their thematic category.

Definition:
Journals are divided into four equal groups based on their impact factor or SJR.

• Q1: Top 25% journals.
• Q2: Journals in the second quartile.
• Q3: Journals in the third quartile.
• Q4: Bottom 25% journals.

Purpose:

• Helps to relativize an impact metric according to the disciplinary field.
• Guides authors in choosing a journal depending on their goals (academic recognition, speed of publication, prestige, etc.).
• Serves as a criterion for some university committees, grant calls, and funding bodies.

Example:
In the Oncology category of the Journal Citation Reports, a Q1 journal is part of the top quartile in terms of impact factor. It will thus be perceived as more influential and attractive than a Q3 or Q4 journal in the same field.

Where to Find This Information Easily?

• Journal Citation Reports for impact factors and associated quartiles.
• SCImago Journal & Country Rank for SJR and quartiles in Scopus.
• Also on PaperDoc: our platform allows you to view at a glance the impact factor, the journal’s ranking in its specialty, and its quartile (Q1 to Q4) when searching for scientific articles.

For example, in the screenshot below from PaperDoc, you can clearly see:

• The journal’s impact factor (4.8)
• Its ranking (18/114 in Nutrition & Dietetics)
• Its position in the first quartile (Q1)

Conclusion

Impact factors and quartiles are essential tools for evaluating the quality and influence of scientific journals. They enable healthcare professionals, researchers and students to guide their reading and publication choices based on objective and comparable criteria. However, it is essential not to consider them in isolation and to take into account the content, scientific relevance and suitability for the research project.