Year	Percent
1990	41.65
1991	41.57
1992	41.5
1993	41.41
1994	41.41
1995	41.49
1996	41.69
1997	41.89
1998	42.1
1999	42.31
2000	42.51
2001	42.72
2002	42.93
2003	43.12
2004	43.31
2005	43.48
2006	43.64
2007	42.37
2008	41.06
2009	39.73
2010	38.37
2011	36.99
2012	35.6
2013	34.19
2014	32.79
2015	32.79
2016	32.82
2017	32.86
2018	32.73
2019	32.62