Year	Percent
1991	20.65
1992	20.204
1993	19.48
1994	17.901
1995	31.676
1996	31.186
1997	30.382
1998	30.708
1999	30.487
2000	30.529
2001	30.284
2002	30.357
2003	29.582
2004	29.384
2005	29.475
2006	25.959
2007	25.953
2008	22.202
2009	21.133
2010	26.139
2011	20.569
2012	19.513
2013	19.453
2014	19.309
2015	19.296
2016	19.253
2017	19.187
2018	19.148
2019	19.105
2020	19.061
2021	19.012
2022	18.964