Year	Percent
1960	3.03626
1961	3.11279
1962	3.13834
1963	3.13006
1964	3.05031
1965	2.9479
1966	2.81899
1967	2.7226
1968	2.70251
1969	2.77135
1970	2.90998
1971	3.03695
1972	3.13258
1973	3.18791
1974	3.1814
1975	3.12837
1976	3.11114
1977	3.05304
1978	2.97447
1979	2.83881
1980	2.67487
1981	2.51751
1982	2.37913
1983	2.29085
1984	2.26236
1985	2.28309
1986	2.28927
1987	2.29388
1988	2.353
1989	2.46846
1990	2.61516
1991	2.78689
1992	2.91831
1993	2.9019
1994	2.71233
1995	2.42279
1996	2.0975
1997	1.84434
1998	1.74414
1999	1.81796
2000	2.0295
2001	2.25839
2002	2.43511
2003	2.54926
2004	2.56968
2005	2.52823
2006	2.48312
2007	2.44796
2008	2.41965
2009	2.38762
2010	2.35945
2011	2.33235
2012	2.29454
2013	2.26006
2014	2.22981
2015	2.19818
2016	2.16792
2017	2.13748