Year	Percent
1960	0.95339
1961	1.12494
1962	1.27872
1963	1.41794
1964	1.50364
1965	1.5572
1966	1.62634
1967	1.66765
1968	1.64623
1969	1.53979
1970	1.36391
1971	1.17396
1972	1.00546
1973	0.94522
1974	0.98705
1975	1.13331
1976	1.30242
1977	1.44888
1978	1.50854
1979	1.51106
1980	1.44874
1981	1.35282
1982	1.29598
1983	1.30058
1984	1.39804
1985	1.55452
1986	1.72607
1987	1.86023
1988	1.88918
1989	1.79827
1990	1.62621
1991	1.41627
1992	1.25427
1993	1.14891
1994	1.16478
1995	1.22961
1996	1.32413
1997	1.38761
1998	1.37841
1999	1.29009
2000	1.13867
2001	0.96065
2002	0.8164
2003	0.75452
2004	0.79079
2005	0.89765
2006	1.02881
2007	1.13078
2008	1.14828
2009	1.05926
2010	0.90687
2011	0.72284
2012	0.57534
2013	0.47076
2014	0.43229
2015	0.44397
2016	0.45549
2017	0.46461