Year	Percent
1971	0.43126
1972	0.44686
1973	0.45476
1974	0.46692
1975	0.47443
1976	0.49106
1977	0.50141
1978	0.51916
1979	0.53723
1980	0.54691
1982	0.5692
1983	0.57479
1984	0.56874
1985	0.5613
1986	0.55208
1987	0.5543
1988	0.55902
1989	0.56499
1990	0.57805
1991	0.58714
1992	0.59417
1994	0.5979
1995	0.61223
1996	0.62012
1997	0.636
1999	0.67229
2000	0.69321
2001	0.70241
2002	0.71575
2003	0.72361
2004	0.73727
2005	0.74599
2006	0.75802
2007	0.75657