Year	Percent
1960	2.29491
1961	2.34664
1962	2.30741
1963	2.59036
1964	2.88183
1965	3.24952
1966	3.819
1967	4.45799
1968	5.17636
1969	5.96905
1970	5.8569
1971	3.04701
1972	2.27537
1973	1.86471
1974	8.75035
1975	12.06919
1976	11.24797
1977	10.18983
1978	11.11321
1979	5.79725
1980	5.34315
1981	8.19038
1982	7.90689
1983	7.09708
1984	6.35485
1985	6.51242
1986	6.07934
1987	5.88911
1988	6.26978
1989	4.55798
1990	3.1777
1991	2.38105
1992	1.94707
1993	1.83569
1994	2.28193
1995	2.35248
1996	2.50413
1997	2.78134
1998	2.91741
1999	2.67078
2000	1.23922
2001	1.33766
2002	1.19848
2003	1.27383
2004	1.51309
2005	1.63784
2006	3.36845
2007	2.81849
2008	2.85857
2009	3.18776
2010	2.86376
2011	2.39093
2012	2.70621
2013	2.18178
2014	2.23599
2015	2.63073
2016	2.78654
2017	3.09926