Year	Percent
1965	23.94
1966	21.45
1967	20.55
1968	20.66
1969	21.52
1970	22.33
1971	21.41
1972	21.73
1973	22.94
1974	21.85
1975	21.3
1976	23.13
1977	21.76
1978	22.71
1979	23.16
1980	23.88
1981	24.47
1982	25.3
1983	25.87
1984	26.28
1985	28.31
1986	27.94
1987	29.21
1988	29.25
1989	29.05
1990	32.48
1991	35.81
1992	37.22
1993	37.15
1994	36.34
1995	35.97
1996	35.25
1997	34.16
1998	32.61
1999	33.63
2000	32.54
2001	33.69
2002	33.31
2003	35.5
2004	32.66
2005	32.36
2006	31.54
2007	29.66
2008	29.97
2009	30.93
2010	31.65