Year	Percent
1960	4.30596
1961	4.21829
1962	4.14251
1963	4.2642
1964	5.01868
1965	4.99268
1966	4.97948
1967	4.95562
1968	4.9397
1969	4.92315
1970	4.91375
1971	4.65438
1972	3.65125
1973	3.65582
1974	3.65892
1975	3.65283
1976	3.64649
1977	3.62676
1978	3.58487
1979	3.52433
1980	3.44558
1981	3.36548
1982	3.29019
1983	3.19962
1984	3.09961
1985	2.99129
1986	2.87861
1987	2.77395
1988	2.70906
1989	2.69188
1990	2.70336
1991	2.7216
1992	2.72512
1993	2.69163
1994	2.6152
1995	2.47159
1996	2.17686
1997	2.08446
1998	1.99069
1999	1.9031
2000	1.81674
2001	1.73194
2002	1.65096
2003	1.5963
2004	1.57216
2005	1.57664
2006	1.66065
2007	1.65909
2008	1.65171
2009	1.62621
2010	1.59262
2011	1.55804
2012	1.52856
2013	1.50256
2014	1.47986
2015	1.46236
2016	1.44635
2017	1.45321