Year	Percent
1968	0.67038
1969	0.67537
1970	0.7544
1971	0.96132
1972	0.84194
1973	0.68345
1974	0.42037
1975	0.4382
1976	0.50447
1977	0.48953
1978	0.51406
1979	0.5914
1980	0.59217
1981	0.51344
1993	0.49477
1994	0.48922
2001	0.15803
2002	0.21638
2003	0.29841
2004	0.57144
2005	0.61163
2006	0.6291
2007	0.59678
2008	0.53565
2009	0.72241
2010	0.69521
2011	0.62052
2012	0.68656
2013	0.77475
2014	0.67314
2015	0.77981
2016	0.92459
2017	0.89117