Anticipating The 2010 Impact Factor — The Devil Is In The Details | The Scholarly Kitchen http://scholarlykitchen.sspnet.org/2011/06/13/anticipating-the-2010-impact-factor/
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The journal impact factor is deceptively simple. A journal’s 2010 impact factor is derived by summing the citations made in 2010 to articles published during the previous two years (i.e,. 2008 and 2009) and dividing this number by the sum of the articles published during those two years