Year	Percent
1960	3.16758
1961	3.09037
1962	3.02216
1963	2.97807
1964	2.96693
1965	2.97757
1966	2.99029
1967	2.99629
1968	3.00922
1969	3.02699
1970	3.04653
1971	3.06178
1972	3.07119
1973	3.07909
1974	3.08347
1975	3.08263
1976	3.07754
1977	3.06107
1978	3.02431
1979	2.96489
1980	2.88927
1981	2.81423
1982	2.74002
1983	2.65441
1984	2.55538
1985	2.45192
1986	2.34026
1987	2.24039
1988	2.17832
1989	2.16394
1990	2.17818
1991	2.20107
1992	2.20539
1993	2.17649
1994	2.10451
1995	2.00387
1996	1.90172
1997	1.81005
1998	1.71884
1999	1.63017
2000	1.54639
2001	1.46048
2002	1.38204
2003	1.32812
2004	1.30467
2005	1.30276
2006	1.30909
2007	1.3105
2008	1.30257
2009	1.28009
2010	1.24765
2011	1.21428
2012	1.18595
2013	1.16114
2014	1.14134
2015	1.12498
2016	1.1101
2017	1.09405