Year	Percent
1971	62.89
1972	63.67
1973	46.84
1974	33.4
1975	38.17
1976	38.35
1977	40.5
1978	38.52
1979	41.61
1980	44.65
1981	30.12
1982	33.28
1983	38.25
1984	34.68
1985	33.63
1986	25.69
1987	30.01
1988	27.89
1989	31.87
1990	34.18
1991	35.95
1992	36.06
1993	38.78
1994	40.18
1995	32.68
1996	39.26
1997	43.15
1998	43.9
1999	47.32
2000	36.06
2001	37.23
2002	41.17
2003	42.21
2004	41.46
2005	39.55
2006	38.05
2007	36.79