In this paper newly established characteristics of the so-called Matthew Effect for Countries (MEC) are presented: field-dependency, time-stability, order of magnitude. We find that the MEC is observable in all main scientific fields that were investigated. Over fifteen years the MEC has been relatively stable. The MEC is a redistribution phenomenon at the macro-level of the sciences. Its magnitude is small; the MEC affects only about five percent of the world production of citations. The MEC, however, crucially impacts many nations when their "national loss of citations" amounts to a high percentage of their expected citations. The relationship between the MEC and Merton's Matthew Principle is discussed. It is our hypothesis that the MEC provides an additional approach for the assessment of the scientific performance of nations.