Year	Percent
1971	0.59904
1972	0.62366
1973	0.64049
1974	0.64772
1975	0.65806
1976	0.66725
1977	0.68089
1978	0.69102
1979	0.70764
1980	0.7197
1981	0.72934
1982	0.73834
1984	0.75664
1985	0.76737
1986	0.78275
1987	0.78967
1988	0.79734
1989	0.80853
1990	0.81709
1991	0.82949
1992	0.84263
1993	0.85443
1994	0.8703
1995	0.88354
1996	0.89517
1997	0.91832
1999	0.94881
2000	0.96405
2001	0.97379
2002	0.97979
2003	0.99016
2004	0.99541
2005	0.99878
2006	1.00074
2007	1.00075
2008	0.98562
2009	0.9784
2010	0.99293
2011	0.99419