Year	Percent
1960	29.357
1961	29.849
1962	30.345
1963	30.846
1964	31.353
1965	31.862
1966	32.377
1967	32.896
1968	33.419
1969	33.946
1970	34.477
1971	35.012
1972	35.675
1973	36.349
1974	37.029
1975	37.714
1976	38.405
1977	39.099
1978	39.798
1979	40.502
1980	41.21
1981	41.92
1982	42.634
1983	43.347
1984	44.063
1985	44.779
1986	45.498
1987	46.219
1988	46.943
1989	47.666
1990	48.391
1991	49.117
1992	49.844
1993	50.569
1994	51.295
1995	51.692
1996	52.022
1997	52.35
1998	52.678
1999	53.007
2000	53.335
2001	53.662
2002	53.99
2003	54.317
2004	54.644
2005	55.174
2006	55.746
2007	56.317
2008	56.886
2009	57.452
2010	58.018
2011	58.581
2012	59.142
2013	59.7
2014	60.256
2015	60.809
2016	61.36
2017	61.908