Year	%
1970	73.34557
1971	73.18856
1972	71.20288
1973	66.68749
1974	67.22735
1975	68.87091
1976	68.02372
1977	68.72187
1978	68.57426
1979	68.17424
1980	67.27833
1981	62.18443
1982	64.52422
1983	66.1475
1984	67.76959
1985	68.34127
1986	67.30071
1987	67.765
1988	67.36833
1989	67.4235
1990	66.75422
1991	67.39863
1992	67.44466
1993	67.23904
1994	68.59524
1995	68.9738
1996	70.25039
1997	71.3331
1998	72.64749
1999	73.52214
2000	74.34097
2001	73.34367
2002	76.48272
2003	78.18344
2004	78.42058
2005	78.99974
2006	79.75437
2007	79.94693
2008	80.23923
2009	80.832
2010	80.87356
2011	79.92303
2012	77.52287
2013	78.21272
2014	78.27538
2015	78.90062
2016	78.80956
2017	77.94505