The impact factor (IF) of an academic journal is a measure reflecting the average number of citations to recent articles published in the journal. It is frequently used as a proxy for the relative importance of a journal within its field, with journals with higher impact factors deemed to be more important than those with lower ones. The impact factor was devised by Eugene Garfield, the founder of the Institute for Scientific Information. Impact factors are calculated yearly starting from 1975 for those journals that are indexed in the Journal Citation Reports.
The journal impact factor (IF) is in widespread use for the evaluation of research and researchers, and considerable controversy surrounds it. The concept behind the IF is citations, and the number of them. The IF is a useful tool for the evaluation of journals, but it must be used carefully. Considerations include the number of review papers, letters or other types of material published in a journal, variations between disciplines, and item-by-item impact. Perhaps the most important use of the IF is in the process of academic evaluation. The extent to which the IF is appropriate for the evaluation of the quality of a specific article or journal and particularly for the evaluation of individual and collective research achievements is highly debatable.
Impact factor- formula
ISI defines the impact factor as a ratio of two elements. The denominator is the total number of “citable” articles published in a particular journal within a given timeframe. The numerator is the total number of citations in the current year to any article published in this journal during that given timeframe. ISI has defined this time frame as two years.
The impact factor (IF) of journal A in a particular year Y is calculated using the following formula:
Method of Calculation
In a given period (Yearly/Half- yearly/ Quarterly/Monthly), the journal impact factor
of a journal is the average number of citations received per paper published in that journal during the one or two (one or more) preceding periods.
For example (Calculation of Journal Impact Factor(JIF) Yearly) , if a journal has an impact factor of 5 in 2009, then its papers published in 2007 and 2008 received 5 citations each on average. The 2009 impact factor of a journal would be calculated as follows:
A = the number of times articles published in 2007 and 2008 were cited by journals, books, patent document, thesis, project reports, news papers, conference/ seminar proceedings, documents published in internet, notes and any other approved documents during 2009.
B = the total number of “citable items” published by that journal in 2007 and 2008. (“Citable items” are usually articles, reviews, proceedings, notes or any other documents pre-reviewed before publishing it).