 Mu buryo bworoshye kumva, ubukene bwari kuba bwaragabanutse kuri icyo gipimo kinini gutya mu gihe igiciro cyo kubaho ku ngo 40 zikennye cyane cyari kuba cyarazamutse ku rwego rwa 4,7 hagati yukwezi kwa mbere 2011 nukwa mbere 2014. 