Year	Percent
1991	33.74
1992	32.548
1993	31.039
1994	29.914
1995	29.468
1996	28.285
1997	29.354
1998	24.937
1999	25.492
2000	23.261
2001	21.923
2002	23.806
2003	20.461
2004	23.046
2005	22.329
2006	22.3
2007	21.956
2008	20.548
2009	22.356
2010	21.683
2011	21.931
2012	21.827
2013	21.713
2014	21.831
2015	20.626
2016	19.779
2017	19.426
2018	18.63
2019	17.86
2020	17.194
2021	16.682
2022	16.185