Year	Percent
1990	31.41
1991	31.36
1992	31.25
1993	31.07
1994	30.81
1995	30.34
1996	29.9
1997	29.45
1998	28.99
1999	28.51
2000	28.04
2001	28.13
2002	28.23
2003	28.32
2004	28.41
2005	28.51
2006	28.21
2007	27.91
2008	27.62
2009	27.32
2010	27.01
2011	26.72
2012	26.46
2013	25.28
2014	24.14
2015	23.03
2016	21.97
2017	20.94
2018	19.94
2019	20.02