Year	Percent
1991	23.485
1992	23.384
1993	23.616
1994	23.472
1995	23.367
1996	23.892
1997	23.419
1998	23.034
1999	23.073
2000	22.78
2001	22.616
2002	22.31
2003	22.973
2004	21.185
2005	20.796
2006	20.956
2007	20.255
2008	19.522
2009	18.771
2010	17.922
2011	17.361
2012	16.377
2013	14.132
2014	14.353
2015	13.762
2016	13.355
2017	13.527
2018	13.561
2019	13.388
2020	13.206
2021	13.046
2022	12.884