Year	Percent
1971	0.53635
1972	0.53238
1973	0.53533
1974	0.54363
1975	0.54317
1976	0.53737
1977	0.52642
1978	0.51538
1979	0.53753
1980	0.51171
1981	0.51115
1988	0.5146
1989	0.51929
1990	0.51958
1991	0.52167
1992	0.53864
1993	0.55807
1996	0.59819
1997	0.6094
1998	0.62038
1999	0.63349
2000	0.63977
2001	0.6472
2002	0.65054
2003	0.66266
2004	0.66825
2005	0.68493
2006	0.69365
2007	0.70219
2008	0.73085
2009	0.74341
2010	0.77322
2011	0.77995
2012	0.79373
2013	0.79762
2014	0.81032
2015	0.81164
2016	0.82139