“…It may be an explanation why these papers focus on a regional market at a time: UK companies [183,26], Italian companies [176,184,185], German companies [186,180,187]. Several classes of assets have been investigated through the clustering and network methodology: market indices (especially stocks) [46,188,189,9,153,190,182], equities [191], currencies [61,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211], commodities [212,213,214,215,216,217,218,219,220,221,222], hous...…”