Year	Percent
1971	21.33
1972	26.3
1973	25.56
1974	26.42
1975	23.21
1976	16.88
1977	15.6
1978	14.33
1979	13.09
1980	13.12
1981	14.34
1982	14.21
1983	14.16
1984	14.22
1985	20.74
1986	21.14
1987	20.36
1988	20.87
1989	21.3
1990	24.11
1991	20.11
1992	21.74
1993	25.2
1994	24.7
1995	23.57
1996	26.8
1997	32.81
1998	35.72
1999	37.27
2000	35.41
2001	30.3
2002	30.29
2003	31.67
2004	31.26
2005	30.67
2006	30.03
2007	29.23
2008	30.35
2009	33.87
2010	34.32