Year	Percent
1960	30.09894
1961	30.77801
1962	31.30915
1963	31.85379
1964	32.40764
1965	32.99853
1966	33.58278
1967	34.11826
1968	34.73046
1969	35.44215
1970	36.15846
1971	36.79066
1972	36.678
1973	36.53067
1974	36.35106
1975	36.13901
1976	36.1388
1977	36.22215
1978	36.37339
1979	36.53208
1980	36.58867
1981	36.67826
1982	36.9099
1983	37.22178
1984	37.55613
1985	37.90727
1986	38.25078
1987	38.64414
1988	39.05178
1989	39.26819
1990	39.60265
1991	39.96829
1992	40.06873
1993	40.22327
1994	40.43501
1995	40.70402
1996	40.87788
1997	41.07465
1998	41.3538
1999	41.65224
2000	41.9319
2001	42.1644
2002	42.4807
2003	42.75745
2004	43.03496
2005	43.31979
2006	43.69203
2007	44.00255
2008	44.26723
2009	44.50424
2010	44.75806
2011	45.04951
2012	45.12824
2013	45.22089
2014	45.34615
2015	45.58758
2016	45.66545
2017	45.73743