Year	Percent
1991	38.45
1992	38.45
1993	38.33
1994	38.3
1995	38.29
1996	38.32
1997	38.34
1998	38.4
1999	38.65
2000	38.83
2001	38.91
2002	39.01
2003	39.14
2004	39.37
2005	39.61
2006	39.62
2007	39.54
2008	39.63
2009	39.44
2010	39.37
2011	39.48
2012	39.7
2013	40
2014	40.47
2015	40.96
2016	41.4
2017	41.85
2018	42.24
2019	42.51
2020	41.39