Year	Percent
1971	0.93563
1976	0.92504
1981	0.92548
1982	0.93509
1983	0.9302
1984	0.93042
1985	0.94636
1986	0.93174
1987	0.92639
1988	0.93177
1989	0.94402
1990	0.94059
1991	0.94696
1992	0.94659
1993	0.95144
1994	0.95534
1995	0.95584
1996	0.96054
1997	0.96565
1998	0.96128
1999	0.96695
2000	0.96969
2001	0.96958
2002	0.96443
2003	0.96342
2004	0.96304
2005	0.96625
2006	0.96986
2007	0.9688
2008	0.96554
2009	0.96514
2010	0.96865
2011	0.97008
2012	0.97176
2013	0.97343
2014	0.97294
2015	0.97333
2016	0.97199