Year	Percent
1990	44.8
1991	44.83
1992	44.89
1993	44.95
1994	45.01
1995	45.05
1996	45.06
1997	45.08
1998	45.1
1999	45.12
2000	45.13
2001	45.12
2002	45.1
2003	45.1
2004	45.51
2005	44.91
2006	44.36
2007	43.74
2008	43.13
2009	43.12
2010	43.03
2011	42.89
2012	42.73
2013	42.53
2014	42.33
2015	42.11
2016	41.85
2017	41.09
2018	40.37
2019	39.68
2020	38.93