Year	%
1972	59.27345
1973	55.75218
1974	56.15285
1975	55.66514
1976	55.63158
1977	55.7926
1978	55.78666
1979	55.93769
1980	55.78497
1981	53.01728
1982	53.37532
1983	53.65373
1984	52.94458
1985	55.5365
1986	56.5503
1987	57.52447
1988	57.90667
1989	58.17553
1990	58.97893
1991	59.17929
1992	60.60057
1993	60.51006
1994	62.33673
1995	64.06114
1996	65.92891
1997	66.78421
1998	69.32083
1999	69.62597
2000	71.181
2001	73.32363
2002	73.86902
2003	75.82079
2004	77.92834
2005	78.88367
2006	79.83114
2007	80.64062
2008	78.23035
2009	79.10233
2010	79.84482
2011	80.69428
2012	80.55838
2013	80.69678
2014	80.20285
2015	80.76135
2016	80.04879
2017	79.96221