Year	%
1975	54.74544
1976	54.50535
1977	54.18668
1978	54.17998
1979	54.29166
1980	53.7983
1981	51.55923
1982	51.74837
1983	51.79414
1984	50.80807
1985	53.64507
1986	55.05206
1987	55.52132
1988	56.02419
1989	57.01786
1990	58.0812
1991	58.00278
1992	59.84719
1993	59.57797
1994	61.63193
1995	63.6709
1996	65.52648
1997	66.37127
1998	68.68775
1999	69.12344
2000	70.6422
2001	72.50853
2002	72.75652
2003	74.93452
2004	76.47522
2005	78.02702
2006	78.6456
2007	79.39823
2008	77.19159
2009	77.93721
2010	78.91845
2011	80.15015
2012	80.1424
2013	80.2995
2014	79.89863
2015	80.14235
2016	79.70665
2017	79.68385