Year	Percent
1960	5.30962
1961	5.27349
1962	5.25219
1963	5.2357
1964	5.24941
1965	5.25389
1966	5.27766
1967	5.2872
1968	5.29512
1969	5.27569
1970	5.25953
1971	5.23627
1972	5.22112
1973	5.20622
1974	5.04601
1975	4.71946
1976	4.73438
1977	4.74076
1978	4.7404
1979	4.72787
1980	4.70349
1981	4.67678
1982	4.64942
1983	4.61855
1984	4.58624
1985	4.54356
1986	4.50371
1987	4.46425
1988	4.38411
1989	4.1321
1990	4.11166
1991	4.08787
1992	4.05994
1993	4.02339
1994	3.98966
1995	3.94942
1996	3.90348
1997	3.85629
1998	3.80822
1999	3.76267
2000	3.71334
2001	3.66099
2002	3.90526
2003	3.85599
2004	3.77942
2005	3.68613
2006	3.60185
2007	3.51598
2008	3.42989
2009	3.33623
2010	3.24895
2011	3.1558
2012	3.07412
2013	2.99837
2014	2.94461
2015	2.89354
2016	2.85027
2017	2.80363