Year	Percent
1960	2.89498
1961	2.92365
1962	2.94939
1963	2.96934
1964	2.98247
1965	2.99233
1966	2.99633
1967	3.00401
1968	3.02838
1969	3.07306
1970	3.12784
1971	3.18489
1972	3.22798
1973	3.24536
1974	3.23156
1975	3.19827
1976	3.15978
1977	3.12977
1978	3.11147
1979	3.10909
1980	3.11646
1981	3.12959
1982	3.13766
1983	3.13325
1984	3.11279
1985	3.08505
1986	3.04091
1987	3.00742
1988	3.02058
1989	3.0911
1990	3.18872
1991	3.30466
1992	3.37984
1993	3.35855
1994	3.22044
1995	3.01612
1996	2.80104
1997	2.63726
1998	2.54812
1999	2.55501
2000	2.62801
2001	2.71025
2002	2.77679
2003	2.84851
2004	2.92044
2005	2.98903
2006	3.05951
2007	3.12232
2008	3.16112
2009	3.17101
2010	3.16094
2011	3.14389
2012	3.12914
2013	3.11619
2014	3.10757
2015	3.10083
2016	3.09245
2017	3.07924