Year	Percent
1960	1.11345
1961	1.10587
1962	1.10435
1963	1.11329
1964	1.13545
1965	1.16928
1966	1.20267
1967	1.24036
1968	1.2995
1969	1.38424
1970	1.48402
1971	1.5923
1972	1.68849
1973	1.75322
1974	1.77692
1975	1.77319
1976	1.75086
1977	1.73761
1978	1.75575
1979	1.81736
1980	1.90153
1981	2.01309
1982	2.09765
1983	2.0908
1984	1.9679
1985	1.78062
1986	1.56175
1987	1.40543
1988	1.39055
1989	1.5622
1990	1.85591
1991	2.18877
1992	2.4629
1993	2.63966
1994	2.68628
1995	2.64882
1996	2.59361
1997	2.57673
1998	2.60314
1999	2.68863
2000	2.81061
2001	2.92522
2002	3.01495
2003	3.09785
2004	3.17096
2005	3.2305
2006	3.29165
2007	3.33486
2008	3.32678
2009	3.25918
2010	3.15701
2011	3.04376
2012	2.95245
2013	2.90096
2014	2.90103
2015	2.93398
2016	2.97197
2017	2.99525