Year	%
1970	83.93552
1971	83.74374
1972	81.83602
1973	80.47866
1974	81.44566
1975	81.67796
1976	79.47131
1977	79.58079
1978	78.25594
1979	78.28094
1980	78.6928
1981	77.42871
1982	75.97251
1983	75.81663
1984	78.68973
1985	78.79322
1986	78.56074
1987	78.14588
1988	77.67732
1989	77.39395
1990	77.49779
1991	77.89714
1992	77.81727
1993	77.52278
1994	78.32446
1995	78.57675
1996	82.31742
1997	79.72586
1998	80.16663
1999	81.58963
2000	81.65469
2001	82.77669
2002	84.12012
2003	85.11672
2004	86.28629
2005	87.18408
2006	89.47364
2007	90.64357
2008	90.77857
2009	91.99543
2010	91.72863
2011	91.71805
2012	92.35399
2013	92.93211
2014	93.56548
2015	94.0147
2016	93.91133
2017	93.04256