Since the impact factor was introduced, it was a controversial issue because many criticizers considered it as an inappropriate and non-scientific indicator. The impact factor is a general measure to assess the validity of a journal but should be cautious about its use.
Consider the difference between disciplines and do not compare the impact factor of them. For instance, psychology is interdisciplinary, and it’s articles use in many disciplines , as a result the journal’s impact factor is often high. But for example, in the nursing field, because that is highly specialized and only researchers in the field use it, its journals also have a low impact factor. Language Difference is another important point, the rate of the impat factor of the English ISI jounals is higher than that of other languages journals and the reason is clear too. In some disciplines, the speed of research is high, such as biology and Immunology, but in some other disciplines, including the humanities, for this subjects an article take a long time to has an effect. For these disciplines, the 5-year impact factor is usually more valid. Some journals publish their articles on the internet free of charge (open access journals), while some other journals must be paid for. This factor can also affect the impact factor.
http://www.donotedit.com/2018/07/25/what-is-the-impact-factor/