Year	Percent
1991	22.214
1992	20.19
1993	20.127
1994	19.274
1995	19.008
1996	18.086
1997	17.09
1998	16.414
1999	16.081
2000	15.875
2001	15.837
2002	15.283
2003	15.78
2004	15.749
2005	16.244
2006	16.657
2007	17.034
2008	18.106
2009	17.783
2010	17.802
2011	18.032
2012	17.903
2013	17.99
2014	17.53
2015	17.282
2016	18.039
2017	17.883
2018	17.819
2019	17.774
2020	17.713
2021	17.639
2022	17.558