Year	Percent
1967	27.21
1968	42.4
1969	60.93
1970	39.27
1971	21.32
1972	20.5
1973	21.66
1974	28.8
1975	18.57
1976	32.62
1977	29.94
1978	30.85
1979	34.19
1980	30.34
1981	40.72
1982	30.93
1983	36.46
1984	52.21
1985	35.53
1986	30.7
1987	33.21
1988	33.5
1989	42.14
1990	37.79
1991	39.25
1992	25.68
1993	34.38
1994	30.32
1995	28.89
1996	36.08
1997	26.1
1998	15.06
1999	34.3
2000	17.73
2001	25.02
2002	18.46
2003	18.15
2004	26.18
2005	24.2
2006	24.26
2007	21.79