Year	Percent
1970	81.18609
1971	81.6
1972	82.03125
1973	82.60038
1974	82.99065
1975	83.3638
1976	83.72093
1977	84.09091
1978	84.58904
1979	85.09213
1980	85.40984
1981	85.8748
1982	86.32075
1983	86.74884
1984	87.02866
1985	87.57396
1986	87.97101
1987	88.47795
1988	88.8424
1989	89.32969
1990	89.78495
1991	90.23747
1992	90.67358
1993	91.09415
1994	91.61452
1995	92.00492
1996	92.49395
1997	92.96782
1998	93.42723
1999	93.87283
2000	94.19795
2001	94.73094
2002	95.13812
2003	95.42982
2004	95.92275
2005	96.2963
2006	96.66319
2007	97.11934
2008	97.36308
2009	97.7978
2010	98.12438
2011	98.34469
2012	98.75
2013	98.95636
2014	99.34396
2015	99.62997