Impact Factor
A metric measuring the average number of citations received by articles in a journal over two years. Higher impact factors indicate greater citation frequency. Results published in high-impact journals (NEJM, Lancet, JAMA) carry more weight in the medical community. Impact factor measures journals, not individual articles.
Technical Context
Impact Factor (IF) = (citations in year Y to articles published in years Y-1 and Y-2) / (number of citable articles published in years Y-1 and Y-2). Example: if a journal published 200 articles in 2023-2024 and those articles received 2,000 citations in 2025, the 2025 IF = 10.0. Top medical journals: New England Journal of Medicine (~176), The Lancet (~168), JAMA (~120). Relevant specialty journals: Diabetes Care (~16), Obesity Reviews (~8), The Lancet Diabetes & Endocrinology (~44). Impact Factor limitations: it is a journal-level metric (not article-level), skewed by a few highly cited articles, manipulable through editorial practices (self-citation, review articles), and varies across disciplines. Article-level metrics (Altmetric score, citation count, h-index for authors) provide complementary assessments. DORA (Declaration on Research Assessment) recommends against using IF as a primary measure of research quality.