Year	Percent
1971	5.527
1972	3.916
1973	1.788
1974	1.464
1975	1.469
1976	1.476
1977	1.476
1978	1.512
1979	1.73
1980	1.89
1981	1.761
1982	1.568
1983	1.612
1984	7.394
1985	6.557
1986	6.398
1987	7.188
1988	7.632
1989	8.01
1990	8.457
1991	8.418
1992	9.685
1993	10.32
1994	11.21
1995	11.03
1996	11.55
1997	12.22
1998	13.92
1999	12.7
2000	12.88
2001	12.64
2002	12.73
2003	13.34
2004	13.78
2005	13.43
2006	12.34
2007	14.23
2008	10.59
2009	10.76
2010	11.32