Year	Percent
1980	24.11
1981	25.43
1982	24.39
1983	25.91
1984	24.54
1985	23.8
1986	22.85
1987	22.3
1988	22.64
1989	25.38
1990	27.53
1991	26.39
1992	31.62
1993	32.01
1995	32.34
1996	32.24
1997	33.67
1998	31.77
1999	31.7
2000	32.18
2001	33.11
2002	31.98
2003	32.02
2004	30.13
2005	29.73
2006	30.26
2007	28.47
2008	28.68
2009	27.01
2010	27.73
2011	29.08
2012	28.56
2013	28.36
2014	28.02
2015	27.52
2016	27.49