Year	Percent
1991	40.63
1992	40.37
1993	40.05
1994	39.75
1995	39.44
1996	39.13
1997	39.08
1998	39.05
1999	39.05
2000	39.14
2001	39.33
2002	39.53
2003	40.68
2004	41.89
2005	41.72
2006	41.19
2007	40.55
2008	38.61
2009	38.39
2010	37.1
2011	37.19
2012	36.78
2013	37.37
2014	36.97
2015	37.75
2016	38.48
2017	39.44
2018	39.53
2019	40.13
2020	37.77