Ein Maß, welches es den Zahlenfetischisten besonders angetan hat, ist der sogenannte Impact Faktor, der heute in großem Stil dazu verwendet wird, die „Qualität“ von Zeitschriften zu berechnen. Der Impact Faktor einer bestimmten Zeitschrift ist ein Quotient, bei dem im Zähler die Anzahl der Zitate in einer Reihe ausgewählter Zeitschriften angegeben ist, die in einem bestimmten Jahr auf Artikel entfielen, welche über einen Zeitraum (meist über die letzten zwei Jahre) in der Zeitschrift erschienen sind. Im Nenner steht die Gesamtzahl der innerhalb des gleichen Zeitraums in der Zeitschrift publizierten Artikel. Ist der Impact Faktor einer Zeitschrift im Jahre 2010 beispielsweise 1,5, dann bedeutet dies, dass ein in dieser Zeitschrift in den Jahren 2008 und 2009 erschienener Artikel im Jahre 2010 im Durchschnitt 1,5 mal zitiert wurde.

Another shortcoming of the journal Impact Factor is its short citation windows, which goes back to convenience and cost-efficiency decisions made in the early days of the SCI (Martyn and Gilchrist 1968; Garfield 1972). Garfield (1972) found that the majority of citations are received within the first 2 years after publication. For some disciplines 2 years are not long enough to attract a significant number of citations, thus leading to large distortions (Moed 2005). Since its 2007 edition, the Journal Citation Report (JCR) includes a 5-year Impact Factor but the 2-year version remains the standard. The asymmetry between numerator and denominator, which was caused by computational limitations in the 1960s and could easily be solved by document-based citation matching, however, still exists.

Central to the introduction of bibliometrics in research evaluation was the creation of the Science Citation Index (SCI) in the 1960s, a citation database initially developed for the retrieval of scientific information. Embedded in this database was the Impact Factor, first used as a tool for the selection of journals to cover in the SCI, which then became a synonym for journal quality and academic prestige. Over the last 10 years, this indicator became powerful enough to influence researchers’ publication patterns in so far as it became one of the most important criteria to select a publication venue. Regardless of its many flaws as a journal metric and its inadequacy as a predictor of citations on the paper level, it became the go-to indicator of research quality and was used and misused by authors, editors, publishers and research policy makers alike.