Year	Percent
1960	54.19995
1961	54.61527
1962	54.66223
1963	54.99893
1964	55.31793
1965	55.63935
1966	55.79005
1967	57.71174
1968	59.41168
1969	60.96052
1970	62.63852
1971	63.45899
1972	63.10312
1973	62.94321
1974	62.16038
1975	62.19234
1976	62.36882
1977	62.30374
1978	62.21858
1979	62.18617
1980	62.07028
1981	61.72776
1982	61.51278
1983	61.55642
1984	61.67589
1985	61.64999
1986	61.4602
1987	61.43004
1988	61.33215
1989	61.19913
1990	61.19933
1991	61.32586
1992	61.23497
1993	61.28799
1994	61.29452
1995	61.21116
1996	61.06445
1997	60.5149
1998	60.01843
1999	59.46843
2000	58.8964
2001	58.24219
2002	58.27182
2003	58.29544
2004	58.36547
2005	58.34166
2006	58.23127
2007	59.02911
2008	59.02114
2009	58.97764
2010	59.23583
2011	59.59518
2012	59.6636
2013	59.74635
2014	59.96522
2015	60.22932
2016	60.4767
2017	60.67034