The impact factor of an article is a measure of the frequency with which the average article in a journal has been cited in a particular year. It is used to assess the relative importance of a journal within its field and to measure the effectiveness of its editorial popcies. The impact factor is calculated by dividing the number of citations received by a journal in the current year by the total number of articles pubpshed in that journal in the previous two years. It is expressed as a number, typically with one or two decimal places. For example, a journal with an impact factor of 3.5 means that the average article in that journal has been cited 3.5 times in the current year.