Year	%
1970	60.24307
1971	60.02666
1972	58.47877
1973	57.2279
1974	57.41864
1975	56.8622
1976	57.21872
1977	56.83905
1978	57.06904
1979	57.2568
1980	56.89939
1981	51.13896
1982	53.2167
1983	53.08541
1984	52.26826
1985	55.42514
1986	56.38502
1987	57.51426
1988	58.79147
1989	59.17167
1990	59.07221
1991	58.48162
1992	59.37771
1993	58.41248
1994	59.93855
1995	61.29554
1996	62.84894
1997	62.38193
1998	65.41468
1999	64.81172
2000	65.96321
2001	66.23225
2002	66.62213
2003	69.4215
2004	72.27621
2005	73.33933
2006	75.92906
2007	77.63054
2008	74.96795
2009	75.80073
2010	76.61391
2011	77.56065
2012	76.65342
2013	77.26583
2014	77.3239
2015	77.62274
2016	76.71728
2017	76.07924