Year	%
1972	61.38968
1973	59.38485
1974	60.37513
1975	59.96101
1976	60.28289
1977	60.42079
1978	60.72191
1979	60.81038
1980	60.57697
1981	56.21979
1982	56.48228
1983	56.91395
1984	55.72972
1985	59.28931
1986	60.22773
1987	61.20756
1988	61.60888
1989	62.87917
1990	62.95534
1991	61.89042
1992	62.64855
1993	61.21755
1994	62.88947
1995	64.39084
1996	66.03177
1997	65.96776
1998	68.89635
1999	68.02204
2000	69.64543
2001	71.13077
2002	72.48767
2003	74.25235
2004	76.66862
2005	77.41592
2006	79.10257
2007	80.26252
2008	77.41755
2009	77.86799
2010	78.64922
2011	79.52071
2012	76.88504
2013	77.28657
2014	76.49097
2015	77.51873
2016	76.35291
2017	76.17916