Year	Percent
1991	35.13
1992	33.11
1993	30.94
1994	28.74
1995	28.21
1996	27.71
1997	26.67
1998	25.58
1999	25.75
2000	25.98
2001	23.85
2002	22.76
2003	21.69
2004	24.14
2005	26.44
2006	28.63
2007	28.11
2008	27.51
2009	26.65
2010	24.99
2011	26.45
2012	28.06
2013	29.68
2014	29.76
2015	29.78
2016	29.49
2017	29.08
2018	28.61
2019	28.11