But impact factor is extremely problematic for many reasons. It's based on citations, which (over the long run) may be an OK measure of impact, but are subject to many confounding factors, including field-specific citation patterns. It's an attempt to predict the success of individual papers on a whole-journal basis, which falls apart in the face of variable editorial decisions. High-impact journals are also often read more widely by people than low-impact journals, which yields a troubling circularity in terms of citation numbers (you're more likely to cite a paper you've read!) Worse, the whole system is prone to being gamed in various ways, which is leading to high rates of retractions for high-impact journals, as well as outright fraud.