Year	Percent
1960	2.76514
1961	2.12641
1962	1.59433
1963	1.39817
1964	1.4725
1965	1.74002
1966	2.07117
1967	2.33455
1968	2.51499
1969	2.55584
1970	2.51253
1971	2.44509
1972	2.4054
1973	3.37233
1974	6.26047
1975	6.06844
1976	5.9122
1977	5.70592
1978	5.45028
1979	5.08847
1980	4.67962
1981	4.22444
1982	3.84882
1983	1.69635
1984	1.19449
1985	1.51293
1986	1.8756
1987	2.18407
1988	2.43494
1989	2.58715
1990	2.67537
1991	2.74658
1992	2.81591
1993	2.52731
1994	2.39872
1995	2.34046
1996	2.26762
1997	2.19286
1998	2.1244
1999	2.06902
2000	2.0206
2001	1.9618
2002	1.61341
2003	1.47906
2004	1.47255
2005	1.48497
2006	1.51239
2007	1.516
2008	1.4537
2009	1.30274
2010	1.10161
2011	0.87815
2012	0.68978
2013	0.59069
2014	0.57479
2015	0.62324
2016	0.687
2017	0.7351