Year	%
1970	73.14721
1971	72.98424
1972	69.75073
1973	66.81512
1974	67.53647
1975	69.60974
1976	68.24918
1977	69.22254
1978	69.40056
1979	68.94458
1980	68.08839
1981	62.21444
1982	65.15194
1983	67.42801
1984	69.92493
1985	69.78396
1986	68.34246
1987	69.15467
1988	68.72511
1989	68.88323
1990	68.04611
1991	68.7528
1992	68.50529
1993	68.77233
1994	69.81884
1995	69.72081
1996	71.14882
1997	72.38467
1998	73.97387
1999	75.03807
2000	76.00612
2001	74.89057
2002	77.88103
2003	79.27434
2004	80.0634
2005	80.62796
2006	81.46482
2007	81.6034
2008	81.61961
2009	82.2676
2010	82.16623
2011	81.069
2012	78.72723
2013	79.38619
2014	79.39664
2015	80.52643
2016	79.81872
2017	78.91964