Year	Percent
1960	25.28715
1961	25.942
1962	26.527
1963	27.09766
1964	27.74588
1965	28.52213
1966	29.42863
1967	30.4866
1968	31.63729
1969	32.75909
1970	33.67557
1971	34.179
1972	34.56637
1973	34.88998
1974	35.24643
1975	35.69075
1976	36.21186
1977	36.80696
1978	37.47045
1979	38.17722
1980	39.2243
1981	41.29698
1982	43.51043
1983	45.86453
1984	48.36433
1985	51.00021
1986	53.79349
1987	56.74922
1988	59.88207
1989	63.18763
1990	65.78315
1991	65.82649
1992	65.91138
1993	65.86527
1994	65.76287
1995	65.66398
1996	65.43615
1997	65.33344
1998	65.46323
1999	65.64189
2000	65.82299
2001	65.60304
2002	65.43945
2003	65.3196
2004	65.22735
2005	65.24279
2006	65.4406
2007	65.74555
2008	66.0525
2009	66.33372
2010	66.58988
2011	67.28321
2012	68.02009
2013	68.72102
2014	69.76823
2015	70.9219
2016	72.22241
2017	73.63415