Martijn P J Loonen1, J Joris Hage, Moshe Kon. 1. Utrecht and Amsterdam, The Netherlands From the Departments of Plastic and Reconstructive Surgery, University Medical Center Utrecht and Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital.
Abstract
BACKGROUND: Citations of articles reflect their scientific relevance. The Institute for Scientific Information's impact factor measures the average number of citations to articles in a journal. Consequently, less-cited articles are credited for the impact that a few frequently cited articles had. Furthermore, the impact factor is only in regard to the citations received in the first 2 years after publication, whereas most articles may be cited only after that period. The authors tested the relevance of the impact factor as a measure of the scientific value of articles. METHODS: The authors identified the 10 most-cited articles of four leading journals and calculated the pattern of their citations over the years. On the basis of the most significant change of regression coefficient in this pattern, they established the critical citable period and the number of citations received in the first 2 years as a fraction of the number of citations received during this period. RESULTS: The citation distribution was skewed. The critical citable period was 16 years, in which articles gathered 61.3 percent of their total number of citations (range, 52.3 to 74.3 percent). The number of citations obtained in the first 2 years correlated well with the number of citations received in the critical citable period (Spearman rho = 0.60, p < 0.001), but only 2.5 percent of the latter number was gathered during the first 2 years (range, 1.2 to 4.0 percent). CONCLUSION: The impact factor is not an adequate indicator for the scientific relevance or impact of the individual articles the authors studied.
BACKGROUND: Citations of articles reflect their scientific relevance. The Institute for Scientific Information's impact factor measures the average number of citations to articles in a journal. Consequently, less-cited articles are credited for the impact that a few frequently cited articles had. Furthermore, the impact factor is only in regard to the citations received in the first 2 years after publication, whereas most articles may be cited only after that period. The authors tested the relevance of the impact factor as a measure of the scientific value of articles. METHODS: The authors identified the 10 most-cited articles of four leading journals and calculated the pattern of their citations over the years. On the basis of the most significant change of regression coefficient in this pattern, they established the critical citable period and the number of citations received in the first 2 years as a fraction of the number of citations received during this period. RESULTS: The citation distribution was skewed. The critical citable period was 16 years, in which articles gathered 61.3 percent of their total number of citations (range, 52.3 to 74.3 percent). The number of citations obtained in the first 2 years correlated well with the number of citations received in the critical citable period (Spearman rho = 0.60, p < 0.001), but only 2.5 percent of the latter number was gathered during the first 2 years (range, 1.2 to 4.0 percent). CONCLUSION: The impact factor is not an adequate indicator for the scientific relevance or impact of the individual articles the authors studied.