Year	Percent
1991	33.508
1992	33.951
1993	33.827
1994	31.598
1995	30.248
1996	28.034
1997	29.462
1998	25.237
1999	26.269
2000	22.954
2001	23.258
2002	23.142
2003	21.789
2004	21.334
2005	20.084
2006	19.395
2007	18.365
2008	18.079
2009	19.158
2010	19.438
2011	18.945
2012	18.934
2013	19.12
2014	19.276
2015	19.22
2016	18.366
2017	18.571
2018	18.394
2019	18.276
2020	18.175
2021	18.066
2022	17.902