Year	Percent
1960	3.06884
1961	3.10953
1962	3.14946
1963	3.18717
1964	3.22234
1965	3.25662
1966	3.28888
1967	3.32398
1968	3.36737
1969	3.42075
1970	3.47931
1971	3.53613
1972	3.58641
1973	3.62989
1974	3.66504
1975	3.69344
1976	3.71231
1977	3.72761
1978	3.74699
1979	3.77239
1980	3.7969
1981	3.8152
1982	3.81783
1983	3.79932
1984	3.75723
1985	3.6983
1986	3.63469
1987	3.57016
1988	3.49936
1989	3.42282
1990	3.34332
1991	3.26661
1992	3.19237
1993	3.11615
1994	3.03783
1995	2.96142
1996	2.88799
1997	2.82454
1998	2.77823
1999	2.75184
2000	2.74014
2001	2.73177
2002	2.72397
2003	2.723
2004	2.72849
2005	2.73727
2006	2.74643
2007	2.75207
2008	2.75156
2009	2.74321
2010	2.72841
2011	2.71183
2012	2.69317
2013	2.66812
2014	2.63612
2015	2.59934
2016	2.56093
2017	2.52311