Year	Percent
1960	4.25347
1961	2.20497
1962	2.11628
1963	2.11941
1964	2.22757
1965	2.39178
1966	2.5735
1967	2.70971
1968	2.83338
1969	2.91324
1970	2.97663
1971	3.06451
1972	3.1297
1973	3.02456
1974	2.71189
1975	2.28333
1976	1.7753
1977	1.37432
1978	1.25941
1979	2.38572
1980	7.03644
1981	7.57413
1982	8.01752
1983	8.27652
1984	8.28023
1985	8.09092
1986	7.88804
1987	7.72034
1988	7.58272
1989	7.48003
1990	7.42431
1991	7.36389
1992	5.126
1993	3.48381
1994	3.35331
1995	3.17494
1996	2.98464
1997	2.83226
1998	2.75636
1999	2.78182
2000	2.86933
2001	2.97473
2002	3.06904
2003	3.14704
2004	3.20622
2005	3.24715
2006	3.29076
2007	3.33327
2008	3.38316
2009	3.43136
2010	3.49072
2011	3.54045
2012	3.57903
2013	3.59018
2014	3.57304
2015	3.53521
2016	3.48794
2017	3.44358