Year	Percent
1991	23.359
1992	23.936
1993	23.341
1994	22.612
1995	22.087
1996	20.862
1997	20.755
1998	20.306
1999	19.281
2000	19.116
2001	18.355
2002	18.054
2003	17.715
2004	17.964
2005	17.071
2006	16.224
2007	16.919
2008	17.465
2009	17.617
2010	16.958
2011	16.456
2012	16.511
2013	17.362
2014	17.419
2015	17.256
2016	16.921
2017	16.524
2018	16.399
2019	16.299
2020	16.213
2021	16.134
2022	16.057