Year	Percent
1960	1.20664
1961	1.37566
1962	1.52955
1963	1.60642
1964	1.5779
1965	1.47877
1966	1.35717
1967	1.27258
1968	1.24393
1969	1.29421
1970	1.3943
1971	1.51535
1972	1.60531
1973	1.63386
1974	1.58067
1975	1.47567
1976	1.33968
1977	1.23093
1978	1.20043
1979	1.27532
1980	1.41329
1981	1.58412
1982	1.70294
1983	1.7006
1984	1.53981
1985	1.27771
1986	0.98215
1987	0.74073
1988	0.59734
1989	0.59093
1990	0.68387
1991	0.79899
1992	0.88299
1993	0.94548
1994	0.97033
1995	0.96589
1996	0.96298
1997	0.96466
1998	0.94418
1999	0.89646
2000	0.83081
2001	0.75544
2002	0.68628
2003	0.63111
2004	0.59787
2005	0.58084
2006	0.56698
2007	0.54873
2008	0.52663
2009	0.49909
2010	0.46708
2011	0.43505
2012	0.40557
2013	0.37995
2014	0.35983
2015	0.34346
2016	0.3275
2017	0.30993