Year	Percent
1971	6.85
1972	11.51
1973	10.73
1974	15.07
1975	12.13
1976	10.51
1977	11.54
1978	10.74
1979	13.46
1980	10.31
1981	12.83
1982	13.82
1983	13.03
1984	13.07
1986	10.58
1987	11.76
1988	11.29
1989	11.93
1990	14.01
1991	15.44
1992	15.75
1993	17.53
1994	18.02
1995	19.76
1996	20.77
1997	19.71
1998	17.7
1999	18.36
2000	19.02
2001	18.82
2002	19.82
2003	19.74
2004	22.19
2005	22.36
2006	21.91
2007	21.88
2008	21.16
2009	20.77
2010	20.64
2011	19.43
2012	19.8
2013	21.16
2014	23.52
2015	23.68
2016	23.68