Year	Percent
1970	0.67048
1971	0.69247
1972	0.7112
1973	0.73311
1974	0.78176
1975	0.81094
1980	0.87493
1981	0.88741
1982	0.89222
1983	0.89181
1984	0.90308
1985	0.89832
1986	0.90552
1987	0.90769
1988	0.91713
1999	0.96661
2000	0.9755
2001	0.96782
2002	0.9507
2003	0.97118
2004	0.94041
2005	0.9584
2006	0.96071
2007	0.9521
2008	0.95952
2009	0.95506