|Impact factor is a key tool which explains the quality of the journal on which it is a rating given to journals based on the number of citations. New journals, which are indexed from their first published issue, will receive an impact factor after two years of indexing; in this case, the citations to the year prior to Volume 1, and the number of articles published in the year prior to Volume 1 are known zero values. Journals that are indexed starting with a volume other than the first volume will not get an impact factor until they have been indexed for three years. Annuals and other irregular publications sometimes publish no items in a particular year, affecting the count. The use of impact factors is extended to evaluate not only the journals, but the papers therein. Journal of Blood Disorders & transfusion has a quality impact factor which is calculated by reflecting the average number of citations to recent articles published in the journal. It is frequently used as a proxy for the relative importance of a journal within its field, with journals with higher impact factors deemed to be more important than those with lower ones.