Year	Percent
1960	3.02305
1961	2.55325
1962	2.16218
1963	2.15889
1964	1.98405
1965	1.72759
1966	1.74327
1967	1.8801
1968	1.7634
1969	1.22505
1970	0.87868
1971	1.40364
1972	1.89323
1973	1.83122
1974	1.75764
1975	1.64818
1976	1.47831
1977	1.42277
1978	1.40299
1979	1.3436
1980	1.37209
1981	1.53707
1982	1.71863
1983	1.71949
1984	1.62406
1985	1.46862
1986	1.32104
1987	1.22476
1988	1.20382
1989	1.24302
1990	1.29878
1991	1.14411
1992	0.91823
1993	0.83393
1994	0.77743
1995	0.7219
1996	0.64866
1997	0.59611
1998	0.56087
1999	0.52418
2000	0.49642
2001	0.45253
2002	0.40615
2003	0.40197
2004	0.45237
2005	0.50279
2006	0.54287
2007	0.58307
2008	0.62292
2009	0.6342
2010	0.86539
2011	1.10967
2012	1.10009
2013	0.79491
2014	0.47228
2015	0.38806
2016	0.34609
2017	0.34934