Year	Percent
1960	3.77624
1961	3.82164
1962	3.83185
1963	3.8352
1964	3.83635
1965	3.85294
1966	3.87854
1967	3.89596
1968	3.91374
1969	3.9383
1970	3.98004
1971	4.03897
1972	4.09352
1973	4.14517
1974	4.19544
1975	4.24488
1976	4.29485
1977	4.34663
1978	4.40663
1979	4.42272
1980	4.39949
1981	4.37701
1982	4.35412
1983	4.3306
1984	4.30866
1985	4.29111
1986	4.2789
1987	4.27171
1988	4.27095
1989	4.2724
1990	4.27255
1991	4.27432
1992	4.27817
1993	4.27948
1994	4.27792
1995	4.27958
1996	4.2838
1997	4.28847
1998	4.29442
1999	4.30228
2000	4.35505
2001	4.36385
2002	4.37376
2003	4.38665
2004	4.39918
2005	4.41108
2006	4.42389
2007	4.43634
2008	4.44581
2009	4.45286
2010	4.47572
2011	4.48346
2012	4.50037
2013	4.52677
2014	4.55401
2015	4.58105
2016	4.60718
2017	4.63071