Year	Percent
1991	18.741
1992	17.874
1993	18.033
1994	17.926
1995	17.983
1996	17.761
1997	17.683
1998	17.341
1999	16.929
2000	16.781
2001	16.395
2002	16.057
2003	16.164
2004	16.43
2005	15.899
2006	15.909
2007	15.995
2008	15.645
2009	15.842
2010	15.105
2011	15.348
2012	15.7
2013	16.009
2014	16.382
2015	16.462
2016	16.73
2017	16.789
2018	17.003
2019	17.312
2020	17.567
2021	17.879
2022	18.176