Year	Percent
1990	37.91
1991	37.62
1992	37.86
1993	37.83
1994	37.75
1995	37.74
1996	37.62
1997	37.53
1998	37.3
1999	37.13
2000	37.19
2001	36.79
2002	36.81
2003	36.6
2004	36.67
2005	36.54
2006	36.61
2007	36.69
2008	36.69
2009	36.66
2010	36.58
2011	36.71
2012	36.91
2013	36.95
2014	36.79
2015	32.09
2016	30.53
2017	29.16
2018	29.01
2019	28.8