Year	Percent
1960	7.73189
1961	6.48053
1962	6.32774
1963	6.28473
1964	6.24491
1965	6.07097
1966	6.55666
1967	6.36428
1968	6.18189
1969	7.00691
1970	8.96448
1971	8.4286
1972	5.98762
1973	3.83917
1974	3.38047
1975	2.56918
1976	2.4007
1977	2.17466
1978	1.78619
1979	1.40734
1980	1.78899
1981	2.50974
1982	2.77905
1983	2.61203
1984	2.22244
1985	2.08612
1986	2.11678
1987	2.23634
1988	2.19876
1989	2.21398
1990	2.60897
1991	2.81611
1992	2.73804
1993	2.81603
1994	2.90312
1995	2.49738
1996	2.22499
1997	2.53055
1998	2.49038
1999	2.48501
2000	2.4846
2001	2.47684
2002	2.46888
2003	2.26856
2004	2.08236
2005	2.49866
2006	2.54215
2007	2.50216
2008	2.46231
2009	2.29762
2010	2.2478
2011	2.5131
2012	2.48839
2013	2.44625
2014	2.31318
2015	2.25717
2016	2.14729
2017	2.02504