Year	Percent
1948	87.1988
1949	86.90217
1950	87.62897
1951	88.37795
1952	88.77953
1953	88.80533
1954	88.36636
1955	88.58758
1956	88.77182
1957	88.62088
1958	88.35857
1959	88.48557
1960	88.55769
1961	88.52938
1962	88.99738
1963	89.39675
1964	89.57118
1965	89.96508
1966	90.48987
1967	91.94646
1968	92.25552
1969	92.23646
1970	92.38982
1971	92.29595
1972	92.52056
1973	92.62936
1974	92.57316
1975	92.49254
1976	92.68798
1977	92.54739
1978	92.54487
1979	92.40131
1980	92.27217
1981	92.28478
1982	92.02809
1983	91.84103
1984	92.01546
1985	92.20937
1986	92.35677
1987	92.2541
1988	92.14841
1989	92.21678
1990	92.23674
1991	92.06983
1992	92.35715
1993	92.1652
1994	92.36613
1995	92.58027
1996	92.6224
1997	92.72664
1998	92.92189
1999	93.17702
2000	93.00281
2001	93.0852
2002	93.21695
2003	92.96296
2004	92.95841
2005	93.05499
2006	93.06556
2007	93.22235
2008	93.43132
2009	93.36102
2010	93.40059
2011	93.64345
2012	93.66018
2013	93.82092
2014	93.94186
2015	93.97806
2016	94.03108
2017	94.12802