Year	Percent
1960	2.44558
1961	2.42576
1962	2.40768
1963	2.39383
1964	2.38533
1965	2.38092
1966	2.37531
1967	2.36939
1968	2.36865
1969	2.37393
1970	2.38191
1971	2.39201
1972	2.39725
1973	2.39028
1974	2.36802
1975	2.33623
1976	2.29616
1977	2.26027
1978	2.24112
1979	2.24404
1980	2.25819
1981	2.27615
1982	2.27888
1983	2.25161
1984	2.18668
1985	2.09735
1986	2.00406
1987	1.92122
1988	1.84743
1989	1.78731
1990	1.73839
1991	1.68966
1992	1.64277
1993	1.61006
1994	1.59419
1995	1.58943
1996	1.58909
1997	1.58488
1998	1.57287
1999	1.54955
2000	1.5181
2001	1.49315
2002	1.47153
2003	1.43683
2004	1.38559
2005	1.32763
2006	1.25855
2007	1.20538
2008	1.20362
2009	1.2684
2010	1.37506
2011	1.48564
2012	1.56838
2013	1.61947
2014	1.62719
2015	1.59801
2016	1.57301
2017	1.5383