Year	Percent
1960	5.1491
1961	5.03441
1962	4.99618
1963	4.95
1964	4.87223
1965	4.76423
1966	4.66371
1967	4.56582
1968	4.47395
1969	4.37343
1970	4.28935
1971	4.23515
1972	4.15719
1973	4.08017
1974	4.02996
1975	3.98808
1976	3.94867
1977	3.89752
1978	3.85454
1979	3.80904
1980	3.76318
1981	3.71045
1982	3.65921
1983	3.58546
1984	3.48782
1985	3.36928
1986	3.25608
1987	3.14461
1988	3.04283
1989	2.94679
1990	2.86206
1991	2.77552
1992	2.69281
1993	2.62019
1994	2.56714
1995	2.52479
1996	2.48712
1997	2.53151
1998	2.47789
1999	2.40194
2000	2.31382
2001	1.83903
2002	1.74153
2003	1.67939
2004	1.61497
2005	1.55113
2006	1.48695
2007	1.42619
2008	1.37692
2009	1.34008
2010	1.31595
2011	1.30638
2012	1.28335
2013	1.25323
2014	1.21914
2015	1.17745
2016	1.13418
2017	1.09432