Year	Percent
1960	3.38017
1961	3.36469
1962	3.33676
1963	3.37451
1964	3.42576
1965	3.48083
1966	3.56232
1967	3.65133
1968	3.68351
1969	3.72622
1970	3.73323
1971	3.72236
1972	3.77294
1973	3.77849
1974	3.81081
1975	3.86719
1976	6.85673
1977	8.96436
1978	9.02037
1979	9.06078
1980	9.13999
1981	9.18766
1982	9.24388
1983	9.27268
1984	9.25886
1985	9.19714
1986	6.54853
1987	4.45884
1988	4.47117
1989	4.47754
1990	4.5001
1991	4.50596
1992	4.52399
1993	4.52835
1994	4.54042
1995	4.55314
1996	4.57257
1997	5.77601
1998	6.72502
1999	6.71871
2000	6.71556
2001	6.68518
2002	6.6756
2003	6.65901
2004	6.66268
2005	6.64808
2006	6.64524
2007	5.91044
2008	5.33754
2009	5.31584
2010	5.29394
2011	5.26878
2012	5.23817
2013	5.20368
2014	5.16926
2015	5.12838
2016	5.08585
2017	5.03262