Year	Percent
1976	40.42
1977	42.4
1978	39.38
1979	35.61
1981	41.28
1982	43.8
1983	50.28
1984	43.48
1985	44.98
1986	44.26
1987	40.74
1988	37.04
1990	33.33
1991	34.75
1992	35.59
1993	33.59
1995	28.33
1996	29.03
1997	28.68
1998	25.19
1999	24.81
2000	23.33
2002	23.97
2003	24.19
2004	21.88
2005	24.81
2006	22.81
2007	24.27
2008	27.37