Year	Percent
1970	25.33885
1971	28.93746
1972	29.44688
1973	32.08946
1974	30.31681
1977	35.22083
1978	34.81777
1979	30.79257
1980	34.52964
1982	31.3544
1983	30.91877
1984	29.32997
1985	31.45047
1986	38.53004
1987	47.65681
1988	48.34704
1989	42.04791
1990	39.55977
1991	42.64164
1992	44.89752
1993	49.23765
1994	54.56632
1995	50.10791
1999	66.80137
2000	65.69253
2001	67.06709
2002	75.32905
2003	75.48331
2004	76.94583
2005	81.03081
2006	80.9089
2007	81.42753
2008	80.595
2010	85.36539