The science citation index impact factor, often shortened to just impact factor or IF, is a measurement for ranking scientific journals based on how frequently the average article published in the journal is cited. It operates as a means to determine the general quality or impact of the selected for publication by different academic journals. Impact factors for each journal are calculated each year.
While a scientific journal's impact factor can be a useful tool for determining the usefulness and prestige of a given journal, many have questioned its reliability. Critics of the impact factor argue that academic journals try to manipulate their impact factor and that the use of impact factors has been detrimental to scientific publication. For example, some suspect that editors have been known to coerce authors, demanding they include unnecessary citations to particular publications in order to bolster their impact factors. Additionally, editors may adjust their publication time tables. Editors may intentionally publish articles at the very start of a calendar year, lengthening the period during which the article is available publicly and increasing the amount of time during which citations to the article count toward the journal's impact factor. Some argue that these methods of manipulating impact factors has shifted too much of the focus in academic publications to prestige.