Year	Percent
1960	28.69395
1961	28.74698
1962	28.8268
1963	28.93985
1964	29.09448
1965	29.29052
1966	29.53672
1967	29.82976
1968	30.16267
1969	30.51944
1970	30.81735
1971	31.03567
1972	31.27368
1973	31.53399
1974	31.82994
1975	32.16637
1976	32.54651
1977	32.96366
1978	33.41884
1979	33.6502
1980	33.60228
1981	33.58653
1982	33.60831
1983	33.64411
1984	33.66562
1985	33.65893
1986	33.60127
1987	33.52023
1988	33.51669
1989	33.39602
1990	33.19585
1991	33.32269
1992	33.73962
1993	34.34901
1994	34.9859
1995	35.51006
1996	35.86146
1997	36.06374
1998	36.14629
1999	36.17575
2000	36.20359
2001	36.2276
2002	36.26676
2003	36.31436
2004	36.37625
2005	36.46624
2006	36.59986
2007	36.76981
2008	36.93538
2009	37.03797
2010	37.03447
2011	36.90861
2012	36.86016
2013	36.81568
2014	36.75775
2015	36.72552
2016	36.7299
2017	36.76224