Year	Percent
1971	9.53
1972	9.465
1973	8.161
1974	7.815
1975	7.565
1976	6.843
1977	5.046
1978	3.331
1979	2.442
1980	2.372
1981	1.866
1982	2.01
1983	5.466
1984	7.038
1985	8.437
1986	7.925
1987	7.994
1988	7.917
1989	8.457
1990	9.54
1991	9.804
1992	9.451
1993	10.12
1994	10.03
1995	10.95
1996	10.18
1997	10.68
1998	10.84
1999	10.9
2000	11.02
2001	11.27
2002	10.98
2003	11.36
2004	10.62
2005	11
2006	10.94
2007	10.74
2008	10.47
2009	10.24
2010	10.29