  Citation metrics are the best tools for research assessments. However,
current metrics may be misleading in research systems that pursue
simultaneously different goals, such as the advance of science and incremental
innovations, because their publications have different citation distributions.
We estimate the contribution to the progress of knowledge by studying only a
limited number of the most cited papers, which are dominated by publications
pursuing this progress. To field-normalize the metrics, we substitute the
number of citations by the rank position of papers from one country in the
global list of papers. Using synthetic series of lognormally distributed
numbers, we developed the Rk-index, which is calculated from the global ranks
of the 10 highest numbers in each series, and demonstrate its equivalence to
the number of papers in top percentiles, P_top0.1% and P_top0.01% . In real
cases, the Rk-index is simple and easy to calculate, and evaluates the
contribution to the progress of knowledge better than less stringent metrics.
Although further research is needed, rank analysis of the most cited papers is
a promising approach for research evaluation. It is also demonstrated that, for
this purpose, domestic and collaborative papers should be studied
independently.
