The Matthew Index - Concentration patterns and Matthew core journals

In this paper we extend our studies to the micro-structure of the Matthew e ffect for countries (MEC). The MEC allows the ranking of countries by their Matthew Index. The rank distribution of countries, observable only at a ma cro-level, has its roots in re-distribution processes of citations in every journal of the database. These re-distributed citations we call Matthew ci tations. Data for 44 countries and 2712 journals (based on the Science Cita tion Index) are analyzed. The strength of the contribution of the individua l journals to the MEC (their number of Matthew citations) is skewly distrib uted. Due to this high concentration of the MEC we are able to define a new type of journal: the Matthew core journal: 145 Matthew core journals accou nt for 50% of the MEG. These journals carry a high potential of gaining a s urplus of citations over what is expected and the risk of losing a high num ber of citations as well.