Year	%
1971	65.99713
1972	65.35717
1973	60.35455
1974	60.44392
1975	59.75388
1976	59.26452
1977	59.15913
1978	58.88164
1979	59.02001
1980	58.41499
1981	55.36368
1982	56.18965
1983	56.07576
1984	55.22045
1985	58.22356
1986	59.31879
1987	59.55414
1988	59.81492
1989	60.46599
1990	61.13858
1991	61.42439
1992	62.83399
1993	62.90101
1994	64.7763
1995	66.51126
1996	68.1047
1997	68.75242
1998	70.75576
1999	70.90796
2000	72.26862
2001	73.59365
2002	74.89175
2003	76.91243
2004	78.71748
2005	80.24974
2006	80.84696
2007	81.19835
2008	79.45915
2009	79.81252
2010	80.43357
2011	81.42664
2012	79.62145
2013	80.76993
2014	80.85241
2015	81.04924
2016	80.65081
2017	80.29609