Year	Percent
1960	23
1961	23.645
1962	24.303
1963	24.973
1964	25.657
1965	26.351
1966	27.057
1967	27.776
1968	28.507
1969	29.247
1970	30
1971	30.72
1972	31.451
1973	32.189
1974	32.937
1975	33.693
1976	34.372
1977	34.718
1978	35.067
1979	35.417
1980	35.769
1981	36.122
1982	36.476
1983	36.832
1984	37.191
1985	37.549
1986	37.909
1987	38.271
1988	38.613
1989	38.755
1990	38.896
1991	39.038
1992	39.18
1993	39.321
1994	39.464
1995	39.606
1996	39.749
1997	39.891
1998	40.034
1999	40.177
2000	40.32
2001	40.464
2002	40.607
2003	40.898
2004	41.306
2005	41.714
2006	42.124
2007	42.535
2008	42.947
2009	43.359
2010	43.773
2011	44.188
2012	44.603
2013	45.019
2014	45.436
2015	45.862
2016	46.296
2017	46.74