Year	%
1970	65.83886
1971	65.46773
1972	63.89513
1973	60.6416
1974	60.63495
1975	60.08668
1976	59.96407
1977	60.35389
1978	60.35745
1979	60.43171
1980	60.23093
1981	56.68657
1982	57.83097
1983	57.93089
1984	57.36966
1985	60.03691
1986	60.72055
1987	61.52547
1988	61.76789
1989	61.94138
1990	62.44455
1991	62.96046
1992	63.8483
1993	64.11541
1994	65.79417
1995	67.28285
1996	68.82238
1997	69.43257
1998	71.71475
1999	71.85784
2000	73.08389
2001	74.47355
2002	75.81313
2003	77.90307
2004	80.03839
2005	81.08519
2006	82.02475
2007	82.36995
2008	80.47437
2009	81.05431
2010	81.57523
2011	82.35566
2012	80.80863
2013	81.59844
2014	81.59359
2015	82.09223
2016	81.37555
2017	80.91385