Year	Percent
1960	4.4829
1961	4.51332
1962	4.54298
1963	4.64765
1964	4.8857
1965	4.87994
1966	4.88475
1967	4.88761
1968	4.92137
1969	4.97007
1970	5.0448
1971	5.12218
1972	5.18784
1973	5.22528
1974	5.25405
1975	4.40118
1976	3.75249
1977	3.77899
1978	3.80089
1979	3.81441
1980	3.81893
1981	3.77291
1982	3.71702
1983	3.74476
1984	3.88691
1985	4.06038
1986	3.94772
1987	3.78529
1988	3.60044
1989	3.00178
1990	2.16967
1991	1.27614
1992	0.56309
1993	0.13807
1994	0.14437
1995	0.48501
1996	0.86493
1997	1.22229
1998	1.79545
1999	2.59517
2000	3.49209
2001	4.4335
2002	5.17115
2003	5.44347
2004	5.1841
2005	4.82018
2006	4.34282
2007	3.84022
2008	3.48649
2009	3.33927
2010	3.33418
2011	3.34466
2012	3.30745
2013	3.26807
2014	3.22818
2015	3.18257
2016	3.14797
2017	3.1385