Year	Percent
1960	34.955
1961	35.344
1962	35.722
1963	36.101
1964	36.483
1965	36.866
1966	37.25
1967	37.636
1968	38.025
1969	38.414
1970	38.804
1971	39.197
1972	39.591
1973	39.985
1974	40.382
1975	40.779
1976	41.179
1977	41.578
1978	41.979
1979	42.381
1980	42.785
1981	43.221
1982	43.738
1983	44.257
1984	44.777
1985	45.298
1986	45.82
1987	46.342
1988	46.867
1989	47.391
1990	47.915
1991	48.469
1992	49.13
1993	49.789
1994	50.449
1995	51.109
1996	51.77
1997	52.428
1998	53.086
1999	53.743
2000	54.399
2001	55.044
2002	55.666
2003	56.287
2004	56.907
2005	57.522
2006	58.137
2007	58.749
2008	59.359
2009	59.964
2010	60.567
2011	61.167
2012	61.763
2013	62.352
2014	62.936
2015	63.514
2016	64.086
2017	64.652