Year	Percent
1968	1.45965
1969	1.37702
1970	1.58426
1971	1.50574
1972	1.86729
1973	1.42057
1974	1.45341
1975	1.74609
1976	2.06736
1977	2.46546
1978	3.22195
1979	3.10479
1980	3.34618
1981	4.33559
1991	4.00222
1992	2.63275
1993	2.10233
1994	1.1895
1995	1.10282
1996	0.9497
1997	0.89467
1998	0.73536
1999	0.71949
2000	0.78275
2001	0.68352
2002	0.86517
2003	0.86074
2004	0.73079
2005	0.7004
2006	0.55125
2007	0.53173
2008	0.50206
2009	0.50275
2010	0.50547
2011	0.52641
2012	0.6659
2013	0.67861
2014	0.68509
2015	0.77608
2016	0.64258
2017	0.60992