Year	Percent
1970	0.60749
1971	0.55482
1975	0.63216
1986	0.79257
1990	0.82121
1991	0.81698
1992	0.81682
1993	0.81897
1994	0.83787
1999	0.88268
2000	0.88985
2002	0.90071
2005	0.91697
2006	0.92117
2007	0.92031
2010	0.9422
2011	0.95775
2012	0.97272