Impact, not impact factor
Editor-in-chief of PNAS Inder Verma states:”When it comes to judging the quality and significance of a body of work, there is no substitute for qualitative assessment. And it bears repeating that the impact factor is not an article-level metric, nor was it intended as a yardstick for comparing researchers’ scholarly contributions. However, at many institutions performance assessments hinge greatly on this number, which currently wields outsize influence on the advancement of scientific careers.”