Year	Percent
1960	2.85389
1961	2.87756
1962	2.8961
1963	2.90961
1964	2.91962
1965	2.92642
1966	2.93083
1967	2.93189
1968	2.93082
1969	2.92877
1970	2.9251
1971	2.92028
1972	2.9147
1973	2.90762
1974	2.90165
1975	2.8936
1976	2.88398
1977	2.87393
1978	2.86996
1979	2.87116
1980	2.87534
1981	2.88184
1982	2.88317
1983	2.8733
1984	2.84792
1985	2.81505
1986	2.78644
1987	2.76501
1988	2.74262
1989	2.72023
1990	2.7015
1991	2.6761
1992	2.66151
1993	2.68815
1994	2.76231
1995	2.86267
1996	2.9708
1997	3.05447
1998	3.09237
1999	3.074
2000	3.01835
2001	2.95908
2002	2.91333
2003	2.87787
2004	2.85709
2005	2.84773
2006	2.83211
2007	2.81689
2008	2.82379
2009	2.8567
2010	2.90232
2011	2.95165
2012	2.98295
2013	2.98183
2014	2.94025
2015	2.87231
2016	2.79806
2017	2.73296