Year	Percent
1960	46.792
1961	47.542
1962	48.294
1963	49.046
1964	49.8
1965	50.649
1966	51.499
1967	52.348
1968	53.197
1969	54.042
1970	54.831
1971	55.552
1972	56.272
1973	56.987
1974	57.7
1975	58.389
1976	59.075
1977	59.756
1978	60.434
1979	61.081
1980	61.693
1981	62.3
1982	62.904
1983	63.504
1984	64.1
1985	64.681
1986	65.258
1987	65.83
1988	66.399
1989	66.718
1990	66.757
1991	66.796
1992	66.835
1993	66.874
1994	66.912
1995	66.951
1996	66.99
1997	67.029
1998	67.067
1999	67.106
2000	67.145
2001	67.183
2002	67.283
2003	67.427
2004	67.597
2005	67.79
2006	67.969
2007	68.147
2008	68.325
2009	68.502
2010	68.596
2011	68.689
2012	68.782
2013	68.875
2014	68.968
2015	69.061
2016	69.154
2017	69.246