Year	Percent
1960	5.44524
1961	5.55639
1962	5.67861
1963	5.80375
1964	5.93215
1965	6.06597
1966	6.20096
1967	6.34619
1968	6.51436
1969	6.70627
1970	6.89407
1971	7.09857
1972	7.31553
1973	7.54574
1974	7.77825
1975	7.99209
1976	8.21586
1977	8.34282
1978	8.34307
1979	8.36525
1980	8.38298
1981	8.3933
1982	8.43122
1983	8.47954
1984	8.53069
1985	8.56981
1986	8.60773
1987	8.65116
1988	8.68824
1989	8.72712
1990	8.79043
1991	8.94701
1992	9.04023
1993	8.99001
1994	8.94081
1995	8.89695
1996	8.86082
1997	8.82498
1998	8.7821
1999	8.73505
2000	8.68578
2001	8.74699
2002	8.85867
2003	8.90186
2004	8.9317
2005	8.96598
2006	8.99809
2007	9.11058
2008	9.24191
2009	9.29739
2010	9.33083
2011	9.35485
2012	9.35718
2013	9.34519
2014	9.33345
2015	9.33069
2016	9.33745
2017	9.34578