Year	Percent
1991	20.4
1992	21.178
1993	21.117
1994	21.005
1995	20.933
1996	20.935
1997	20.046
1998	20.352
1999	21.067
2000	20.708
2001	19.799
2002	19.318
2003	19.337
2004	19.252
2005	18.592
2006	17.721
2007	17.288
2008	17.331
2009	16.527
2010	16.315
2011	16.836
2012	16.71
2013	15.478
2014	15.314
2015	14.85
2016	17.924
2017	17.808
2018	17.562
2019	17.34
2020	17.204
2021	17.09
2022	16.958