<P> Indeed, impact factors are sometimes used to evaluate not only the journals but the papers therein, thereby devaluing papers in certain subjects . The Higher Education Funding Council for England was urged by the House of Commons Science and Technology Select Committee to remind Research Assessment Exercise panels that they are obliged to assess the quality of the content of individual articles, not the reputation of the journal in which they are published . The effect of outliers can be seen in the case of the article "A short history of SHELX", which included this sentence: "This paper could serve as a general literature citation when one or more of the open - source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal - structure determination". This article received more than 6,600 citations . As a consequence, the impact factor of the journal Acta Crystallographica Section A rose from 2.051 in 2008 to 49.926 in 2009, more than Nature (at 31.434) and Science (at 28.103). The second-most cited article in Acta Crystallographica Section A in 2008 only had 28 citations . Also, impact factor is a journal metric and should not be used to assess individual researchers or institutions . </P> <P> Journal rankings constructed based solely on impact factors only moderately correlate with those compiled from the results of expert surveys . </P> <P> A.E. Cawkell, sometime Director of Research at the Institute for Scientific Information remarked that the Science Citation Index (SCI), on which the impact factor is based," would work perfectly if every author meticulously cited only the earlier work related to his theme; if it covered every scientific journal published anywhere in the world; and if it were free from economic constraints ." </P> <P> A journal can adopt editorial policies to increase its impact factor . For example, journals may publish a larger percentage of review articles which generally are cited more than research reports . Thus review articles can raise the impact factor of the journal and review journals will therefore often have the highest impact factors in their respective fields . Some journal editors set their submissions policy to "by invitation only" to invite exclusively senior scientists to publish "citable" papers to increase the journal impact factor . </P>

Whats a good impact factor for a journal