Year	Percent
1960	3.35178
1961	3.37926
1962	3.38206
1963	3.35031
1964	3.28343
1965	3.19627
1966	3.09757
1967	3.00847
1968	2.9401
1969	2.90227
1970	2.88257
1971	2.86454
1972	2.83891
1973	2.80871
1974	2.77141
1975	2.72875
1976	2.69369
1977	2.66042
1978	2.61682
1979	2.56017
1980	2.49862
1981	2.43707
1982	2.38955
1983	2.37125
1984	2.38788
1985	2.42739
1986	2.44934
1987	2.46197
1988	2.50911
1989	2.59834
1990	2.69896
1991	2.81611
1992	2.87853
1993	2.80517
1994	2.56749
1995	2.22866
1996	1.8718
1997	1.56834
1998	1.3312
1999	1.18599
2000	1.11329
2001	1.05613
2002	1.00113
2003	0.98728
2004	1.01841
2005	1.0836
2006	1.15977
2007	1.24032
2008	1.3385
2009	1.45196
2010	1.57029
2011	1.69283
2012	1.79623
2013	1.85142
2014	1.84568
2015	1.79568
2016	1.73252
2017	1.673