Year	Percent
1960	25.537
1961	26.144
1962	26.234
1963	26.323
1964	26.413
1965	26.502
1966	26.592
1967	26.682
1968	26.773
1969	26.863
1970	26.954
1971	27.045
1972	27.136
1973	27.227
1974	27.319
1975	27.41
1976	27.502
1977	27.594
1978	27.687
1979	27.779
1980	27.872
1981	27.965
1982	28.058
1983	28.151
1984	29.028
1985	29.94
1986	30.871
1987	31.817
1988	32.78
1989	33.755
1990	34.745
1991	35.748
1992	36.766
1993	37.792
1994	38.831
1995	40.494
1996	42.187
1997	43.893
1998	45.616
1999	47.35
2000	49.092
2001	50.832
2002	52.573
2003	54.307
2004	56.033
2005	57.74
2006	59.431
2007	61.1
2008	62.745
2009	64.358
2010	65.94
2011	67.488
2012	69
2013	69.544
2014	70.083
2015	70.616
2016	71.138
2017	71.646