Year	%
1971	62.5862
1972	60.63521
1973	59.13438
1974	58.81318
1975	57.98933
1976	57.75051
1977	57.10514
1978	56.50005
1979	56.65947
1980	55.73779
1981	50.6929
1982	52.18736
1983	51.79808
1984	50.65806
1985	54.33735
1986	55.72731
1987	56.13949
1988	57.61495
1989	58.73275
1990	58.74266
1991	57.53245
1992	59.15395
1993	57.55787
1994	59.34471
1995	60.92935
1996	62.37618
1997	61.6374
1998	63.9579
1999	63.2886
2000	64.60045
2001	65.02193
2002	64.89758
2003	67.85561
2004	70.33852
2005	71.9762
2006	74.21649
2007	75.84504
2008	73.3309
2009	73.90382
2010	74.91284
2011	76.02427
2012	74.80349
2013	75.95689
2014	76.20036
2015	76.13427
2016	75.6931
2017	75.17031