Year	number
2005	21.52
2006	20.365384615384617
2007	19.654545454545456
2008	19.571428571428573
2009	19.267857142857142
2010	18.839285714285715
2011	18.96551724137931
2012	16.593220338983052
2013	15.832258064516129
2014	15.364516129032259
2015	14.864516129032259
2016	14.76774193548387
2017	14.8
2018	14.485714285714286
2019	13.81904761904762