Evaluation of the Relevance of Research Articles Published 50 Years Ago in Key Scientific Journals in the USA, England and Germany: Introduction of 50 Years Impact Index in Addition to Impact Factor

The aim of this study was to assess the current applicability of articles that show important advances in medicine. The recruited papers include those published fifty years ago in the most respected journals in the USA, England and Germany. Using PubMed Central citations since 2010, original articles closely related to papers published in 1966 in the New England Journal of Medicine (NEJM), the Lancet and the Deutsche Medizinische Wochenschrift (DMW) were identified. In the NEJM, there were 163 observational articles, 18 clinical, and 117 case reports. In the Lancet, there were 390 observational articles, 29 diagnostic, 82 therapeutic, 38 animal, 28 in vitro studies and 61 case reports. In the DMW, there were 77 observational articles, 39 therapeutic, 28 diagnostic, 7 animal, 4 in vitro, 9 other studies and 57 case reports. The number of highly relevant articles still currently cited were determined as 12/298 (4%) in the NEJM, 11/ 628 (1.7%) in the Lancet and 1/221 (0.45%) in the DMW (0.45%). It was concluded that "halfhundred years impact index" should be regarded as a measure of ‘relevance and quality over time’. Combined with impact factor, it could be a better indicator for importance of scientific journals.