Year	Percent
1990	37.22
1991	36.7
1992	36.2
1993	35.72
1994	35.25
1995	34.3
1996	33.38
1997	32.47
1998	31.58
1999	30.9
2000	30.22
2001	29.52
2002	28.84
2003	28.16
2004	28.52
2005	28.24
2006	27.97
2007	27.7
2008	27.45
2009	27.19
2010	26.95
2011	26.76
2012	26.58
2013	27.78
2014	28.86
2015	29.72
2016	29.69
2017	30.9
2018	30.54
2019	30.89