Year	Percent
1991	39.21
1992	38.93
1993	38.63
1994	38.45
1995	38.15
1996	37.85
1997	37.57
1998	37.28
1999	36.93
2000	36.71
2001	36.63
2002	36.49
2003	36.38
2004	36.32
2005	36.27
2006	34.96
2007	33.65
2008	32.32
2009	30.66
2010	29.22
2011	27.83
2012	26.48
2013	25.47
2014	24.55
2015	23.66
2016	22.82
2017	22.06
2018	21.32
2019	20.83