How Impact Factors are Calculated
A journal's impact factor for 2012 is calculated by taking the number of citations in 2012 from articles that were published in 2011 and 2010 and dividing that number by the total number of articles published in that same journal in 2011 and 2010. Please see the example below.
The specific calculations for Nursing Research's 2011 impact factor are displayed below.
Articles published in 2010 that were cited in 2011: 63
Articles published in 2009 that were cited in 2011: 94
Total Number of articles published in 2010: 61
Total number of articles published in 2009: 51
157 (articles published in 2010 and 2009 that were cited in 2011)
112 (total number of articles published in 2010 and 2009)
The 2011 Impact Factor for the journal Nursing Research means that, on average, articles published in this journal from one or two years ago have been cited around 1.4 times.
The information above appears in a Michigan State University Library research guiide.