We investigated the grouping properties of industry sectors in the complex networks based on stock data for US and Korean stock markets. The complex networks are constructed by the minimal spanning tree (MST). We propose a novel approach based on the shortest path length
(SPL) between stocks to quantify the grouping properties of industry sectors. We found that the grouping coefficients for the United States have a higher value than those of the Korean stock market. In particular, for the Korean stock market, the conglomerates, which are made up of
companies belonging to diverse industry sectors, have significant grouping coefficients.
PACS numbers: 87.10.+e, 89.20.-a, 87.90.+y
Keywords: complex network, minimum spanning tree, grouping coefficient
