Year	Percent
1960	1.22961
1961	1.33785
1962	1.41247
1963	1.41151
1964	1.31443
1965	1.15484
1966	0.96476
1967	0.80206
1968	0.70573
1969	0.7039
1970	0.76555
1971	0.85218
1972	0.90822
1973	0.90608
1974	0.8221
1975	0.68462
1976	0.53113
1977	0.40797
1978	0.33453
1979	0.3318
1980	0.38053
1981	0.44181
1982	0.48976
1983	0.53128
1984	0.55846
1985	0.57372
1986	0.59161
1987	0.61057
1988	0.61377
1989	0.59683
1990	0.56576
1991	0.07944
1992	0.49724
1993	0.43329
1994	0.37223
1995	0.36125
1996	0.35408
1997	0.35375
1998	0.3686
1999	0.51446
2000	0.68493
2001	0.72779
2002	0.72723
2003	0.70878
2004	0.73631
2005	0.7538
2006	0.69721
2007	0.6187
2008	0.55886
2009	0.51449
2010	0.49403
2011	0.48365
2012	0.48398
2013	0.51477
2014	0.47981
2015	0.41724
2016	0.39924
2017	0.38645