Year	Percent
1960	3.34549
1961	3.33725
1962	3.31861
1963	3.27726
1964	3.20852
1965	3.12478
1966	3.03817
1967	2.96505
1968	2.91342
1969	2.88874
1970	2.88193
1971	2.88043
1972	2.87368
1973	2.86091
1974	2.83913
1975	2.8123
1976	2.78461
1977	2.76204
1978	2.74754
1979	2.74301
1980	2.74418
1981	2.74409
1982	2.73928
1983	2.73164
1984	2.7203
1985	2.70484
1986	2.68872
1987	2.66861
1988	2.63775
1989	2.59441
1990	2.54304
1991	2.48883
1992	2.43748
1993	2.39108
1994	2.35169
1995	2.31699
1996	2.27979
1997	2.24028
1998	2.20495
1999	2.17465
2000	2.14585
2001	2.12336
2002	2.09519
2003	2.04394
2004	1.96361
2005	1.86694
2006	1.76377
2007	1.67598
2008	1.62004
2009	1.60575
2010	1.61957
2011	1.6416
2012	1.65369
2013	1.65288
2014	1.63282
2015	1.5996
2016	1.5645
2017	1.53468