In 1955, Garfield suggested that the number of references could be used to measure the "impact" of a journal, but the term "impact factor" was introduced in 1963 by Garfield and Sher. The primary goal of impact factor analysis was to improve the management of library journal collections. Single-parameter measurements of the quality of a journal article have become increasingly popular as a substitute for scientific quality. The simplicity of its counting system and convenience of its use are significant benefits. Probably for these reasons, funding bodies, academic authorities, and some governments began using the impact factor to guide decisions about allocating grants, awarding appointments and academic degrees, and defining scientific policy. The journal impact factor, which is often recognized as a symbol of scientific prestige and relevance, can be, however, greatly influenced by the type of medical article (review vs original work), clinical specialty, and research. The true value and implications of the journal impact factor (JIF) are important to understand. It is critical to remember that JIF can be used only to evaluate journals. All comparisons should include only journals and never individuals or departments. Only similar journals (particularly those dedicated to the same scientific specialty) must be compared, because the value of the impact factor varies greatly by discipline.