Year	Percent
1970	0.80627
1971	0.80042
1972	0.79936
1973	0.78689
1974	0.77271
1975	0.81687
1976	0.83696
1977	0.837
1978	0.83965
1981	0.84002
1982	0.85875
1983	0.89788
1984	0.90076
1988	0.90849
1989	0.92303
1990	0.93065
1991	0.93871
1992	0.94584
1993	0.92808
1994	0.93455
1995	0.93194
1996	0.93167
1999	0.96488
2000	0.9703
2001	0.97833
2002	0.98068
2003	0.98267
2004	0.98663
2005	0.97537
2006	0.98306
2007	0.98176
2008	0.98895
2009	0.98846
2010	1.02716
2011	1.02839
2012	1.01363
2013	0.989
2014	0.9855
2015	0.98705
2016	0.99525