Year	%
1970	94.03027
1971	94.02356
1972	93.97257
1973	94.217
1974	94.59571
1975	95.42797
1976	95.3956
1977	95.99098
1978	96.31757
1979	96.61421
1980	96.94239
1981	96.72236
1982	96.63605
1983	97.04254
1984	97.33066
1985	97.60895
1986	97.43737
1987	97.22342
1988	97.1155
1989	97.03797
1990	97.00618
1991	97.21383
1992	97.59305
1993	97.43021
1994	97.26067
1995	97.44347
1996	97.52471
1997	97.58393
1998	97.65853
1999	97.75339
2000	97.9692
2001	97.92354
2002	97.91513
2003	97.9031
2004	97.98646
2005	97.97586
2006	97.93105
2007	98.04894
2008	98.07433
2009	98.06525
2010	98.07721
2011	98.06477
2012	98.10758
2013	98.16835
2014	97.75039
2015	98.0698
2016	98.11119
2017	98.09685