Year	Percent
1971	0.50144
1972	0.51646
1974	0.5525
1975	0.55843
1976	0.57289
1977	0.57915
1978	0.591
1979	0.60189
1980	0.60872
1981	0.61814
1982	0.6309
1983	0.64322
1984	0.64488
1985	0.6505
1986	0.6524
1987	0.65638
1988	0.65793
1989	0.66295
1990	0.69238
1991	0.70085
1992	0.70482
1993	0.71472
1994	0.72684
1995	0.74037
1996	0.75085
1997	0.76191
1998	0.7803
1999	0.80805
2000	0.83163
2001	0.85423
2002	0.868
2003	0.87972
2004	0.88381
2005	0.8865
2006	0.88983
2007	0.89509
2008	0.89837
2009	0.90522
2010	0.91258
2011	0.91378
2012	0.91305