In the world of academic research, the question "Where is this paper indexed?" is a critical measure of a study's impact and quality. Among the dozens of databases, SCI, EI, and Scopus are recognized globally as the top three most prestigious academic literature indexes.

However, these three are not interchangeable. Each has a distinct history, indexing focus, and evaluation system. Whether you are a new graduate student or a seasoned scholar, clearly understanding their differences is essential for effective literature reviews and for strategically targeting your own publications.

1. SCI (Web of Science): The "Gold Standard" for Basic Science

• Full Name: Science Citation Index, now primarily known as SCIE (Science Citation Index Expanded).
• Platform: Web of Science (WoS) Core Collection
• Owner: Clarivate

SCI is one of the oldest and most authoritative citation databases. Its core value lies in its rigorous journal selection process and its unique "citation analysis."

Indexing Scope & Focus:

• Subjects: Its traditional strengths are in the basic sciences and life sciences, such as physics, chemistry, biology, medicine, and materials science.
• Document Types: It is overwhelmingly focused on high-quality academic journals (Journal Articles). The SCI selection process is extremely strict, and being indexed is a symbol of a journal's quality. It indexes very few conference papers.

Key Evaluation Metrics:

• Journal Impact Factor (IF): This is SCI's "crown jewel" metric, published annually in the Journal Citation Reports (JCR). The IF is the global standard for measuring a journal's average citation impact.
• JCR Quartiles (Q1-Q4): Journals in the same subject category are ranked by their IF, with the top 25% placed in Q1, and so on. Q1 journals are widely considered the top-tier publications in their field.

In a sentence: SCI is the benchmark of authority for basic sciences, centered on high-quality journals and driven by the Impact Factor.

2. EI (Engineering Index): The "Industry Cornerstone" for Engineering

• Full Name: Engineering Index
• Core Database: Compendex
• Platform: Engineering Village
• Owner: Elsevier

EI is the world's most authoritative database for engineering and technology. If SCI is the standard for scientists, EI is the bible for engineers.

Indexing Scope & Focus:

• Subjects: Exclusively focused on all fields of engineering, including computer science, electrical engineering, mechanical engineering, civil engineering, chemical engineering, and aerospace.
• Document Types: This is the biggest difference from SCI. EI places equal importance on journal articles (JA) and high-quality conference papers (CA).

Core Features:

• Focus on Conferences: In Computer Science (CS) and many engineering fields, publishing in top conferences is the primary way to disseminate cutting-edge research. EI understands this and indexes a vast number of authoritative technical conferences, making it an indispensable tool for CS/EE professionals.

In a sentence: EI is the go-to database for engineering, and its inclusion of conference papers is critical for computer science and technical fields.

3. Scopus: The Largest & Most Comprehensive "Challenger"

• Full Name: Scopus
• Owner: Elsevier (same as EI)

Launched in 2004, Scopus is Elsevier's direct competitor to Web of Science (SCI). Its core advantages are its massive scale and comprehensive scope.

Indexing Scope & Focus:

• Subjects: The broadest of all three. It not only provides excellent coverage of STEM fields but also heavily indexes the Social Sciences, Arts & Humanities, and Economics.
• Document Types: Its coverage is vast, including journals, conference papers, book series, and trade publications.
• Global Reach: Scopus has a stronger representation of non-English journals (especially from Europe and Asia) compared to Web of Science.

Key Evaluation Metrics:

• CiteScore: This is Scopus's journal-level metric designed to compete with SCI's Impact Factor.
• h-index: Scopus provides powerful author-profiling tools and is one of the most common platforms used to calculate an individual researcher's h-index.

In a sentence: Scopus is the largest and most interdisciplinary database, covering the social sciences and humanities, and is the go-to tool for measuring a scholar's h-index.

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At-a-Glance: SCI vs. EI vs. Scopus

Feature	SCI (Web of Science Core Collection)	EI (Compendex)	Scopus
Owner	Clarivate	Elsevier	Elsevier
Core Focus	Authority, Depth, Basic Science	Engineering & CS Specialist	Breadth, Scale, Interdisciplinary
Subject Scope	Natural Sciences, Medicine, (Eng)	Engineering & Technology Only	Broadest (STEM, Social Sci, Arts)
Document Types	High-Impact Journals	Journals & Conference Papers	Journals, Conferences, Books
Key Metrics	Impact Factor (IF), JCR Quartiles	Compendex Indexing	h-index (Author), CiteScore (Journal)
Best For	Basic Scientists, Medical Doctors	Engineers, Computer Scientists	Interdisciplinary & Social Scientists, Institutional Analysts

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Conclusion: Which One Should You Choose?

• If you are in Basic Science (Physics, Chemistry, Biology, Medicine): SCI (WoS) is your primary benchmark and the gold standard for your field.
• If you are in Engineering or Computer Science: EI is crucial, especially if you are publishing in top-tier conferences. Scopus is also highly relevant due to its broad coverage and h-index tracking.
• If you are in the Social Sciences or Humanities: Scopus is your best choice, as it offers far more comprehensive coverage in these fields than SCI.
• For a Comprehensive Literature Review: It is best practice to use both Scopus and Web of Science to ensure you don't miss any relevant literature.