Year	%
1970	56.36474
1971	56.17915
1972	54.5131
1973	53.74142
1974	54.1576
1975	54.26961
1976	53.11419
1977	53.05174
1978	53.31433
1979	53.47279
1980	52.55347
1981	48.01951
1982	48.69859
1983	47.64599
1984	47.60528
1985	48.59421
1986	49.29004
1987	49.91331
1988	51.46217
1989	51.922
1990	51.68903
1991	51.54969
1992	51.04988
1993	50.4804
1994	51.06373
1995	51.94779
1996	52.84441
1997	52.454
1998	54.42438
1999	54.51501
2000	57.05317
2001	58.99028
2002	61.20587
2003	63.7382
2004	65.19498
2005	66.38171
2006	68.56577
2007	70.53423
2008	70.34735
2009	71.24079
2010	72.18637
2011	72.21863
2012	72.24645
2013	72.81561
2014	72.76493
2015	73.03315
2016	72.29078