Year	Percent
1971	11.11
1972	10.82
1973	10.49
1974	11.61
1976	14.96
1977	14.65
1978	12.85
1979	10.28
1981	12.97
1982	13.48
1983	16.73
1984	15.22
1985	15.54
1986	13.99
1987	13.1
1988	11.17
1990	11
1991	13.57
1992	13.3
1993	13.32
1995	10.77
1996	11.62
1997	12.21
1998	12
1999	9.52
2000	7.46
2002	10.55
2003	10.82
2004	8.6
2005	10.08
2006	10.42
2007	9.53
2008	9.66
2009	12.5
2010	12.7
2011	12.8
2012	12
2015	9.7