Year	Percent
1960	3.15183
1961	3.14591
1962	3.1372
1963	3.12485
1964	3.109
1965	3.09232
1966	3.06309
1967	3.03697
1968	3.04041
1969	3.08019
1970	3.13608
1971	3.19438
1972	3.22276
1973	3.19725
1974	3.10694
1975	2.97487
1976	2.8365
1977	2.71282
1978	2.59799
1979	2.49764
1980	2.40936
1981	2.32471
1982	2.24299
1983	2.17178
1984	2.11248
1985	2.06366
1986	2.01347
1987	1.96815
1988	1.9447
1989	1.94717
1990	1.96389
1991	1.98771
1992	1.99756
1993	1.97538
1994	1.91173
1995	1.82031
1996	1.73076
1997	1.65241
1998	1.57035
1999	1.48567
2000	1.40493
2001	1.31592
2002	1.24245
2003	1.2237
2004	1.27462
2005	1.37066
2006	1.48256
2007	1.57168
2008	1.61908
2009	1.60883
2010	1.55804
2011	1.49834
2012	1.44909
2013	1.4034
2014	1.36625
2015	1.3349
2016	1.30173
2017	1.2644