Year	Percent
1960	3.39735
1961	3.25907
1962	3.28475
1963	3.21663
1964	3.21347
1965	2.97306
1966	3.11259
1967	3.13458
1968	3.11509
1969	2.93181
1970	2.91864
1971	2.89893
1972	2.88076
1973	2.83531
1974	2.76142
1975	3.06503
1976	3.09337
1977	3.14325
1978	3.26152
1979	3.26135
1980	3.2502
1981	3.36605
1982	3.26994
1983	3.19141
1984	3.0079
1985	2.93123
1986	2.95377
1987	2.90179
1988	2.62875
1989	2.46085
1990	2.35544
1991	2.28769
1992	1.83233
1993	1.73597
1994	1.67714
1995	1.56575
1996	1.5401
1997	1.47698
1998	1.46392
1999	1.38584
2000	1.34121
2001	1.27651
2002	1.21571
2003	1.21499
2004	1.14927
2005	1.09156
2006	1.05124
2007	1.09453
2008	1.2139
2009	1.16004
2010	1.08463
2011	1.04351
2012	1.03819
2013	1.01192
2014	0.9763
2015	0.92359
2016	0.92526
2017	0.90949