Year	number
2005	18.529411764705884
2006	17.057142857142857
2007	16.8
2008	15.028571428571428
2009	14.342857142857143
2010	13.971428571428572
2011	13.142857142857142
2012	11.82857142857143
2013	11.700000000000001
2014	11.726315789473684
2015	10.805263157894737
2016	10.700000000000001
2017	10.726315789473684
2018	10.700000000000001
2019	10.121052631578948