Year	Percent
1990	37.73
1991	37.73
1992	37.73
1993	37.7
1994	37.66
1995	37.6
1996	37.59
1997	37.58
1998	37.56
1999	37.53
2000	37.48
2001	37.45
2002	37.43
2003	37.39
2004	37.34
2005	37.28
2006	37.23
2007	37.17
2008	37.07
2009	36.94
2010	36.82
2011	36.73
2012	38.33
2013	35.55
2014	36.69
2015	35.34
2016	35.58
2017	36.96
2018	36.93
2019	36.92