Year	%
1971	58.28004
1972	56.07132
1973	55.16205
1974	55.14425
1975	54.69544
1976	53.87125
1977	53.18569
1978	52.85694
1979	52.97529
1980	51.71719
1981	48.03506
1982	48.27097
1983	46.99672
1984	46.26438
1985	47.32509
1986	48.32055
1987	48.76955
1988	50.37989
1989	51.16274
1990	51.34111
1991	50.71896
1992	50.46099
1993	49.61578
1994	50.35817
1995	51.39758
1996	52.23621
1997	51.71063
1998	53.09055
1999	53.32316
2000	56.02378
2001	58.06995
2002	59.81945
2003	62.70645
2004	63.71139
2005	65.18517
2006	67.32521
2007	68.96468
2008	68.54542
2009	69.54282
2010	70.61283
2011	71.07797
2012	71.31306
2013	71.97256
2014	72.10079
2015	72.15037
2016	71.83307