Year	Percent
1960	3.10455
1961	3.21376
1962	3.28178
1963	3.24978
1964	3.17374
1965	2.99122
1966	1.75938
1967	1.71255
1968	3.79864
1969	3.98644
1970	4.37983
1971	10.75299
1972	10.95524
1973	10.95782
1974	10.8008
1975	10.52053
1976	10.19343
1977	9.9202
1978	7.81822
1979	5.92621
1980	6.14088
1981	6.34366
1982	6.48813
1983	6.55192
1984	6.50439
1985	5.71681
1986	3.7915
1987	3.6933
1988	3.58211
1989	3.45464
1990	3.14182
1991	2.63831
1992	2.51945
1993	2.36913
1994	2.18852
1995	2.45222
1996	3.47578
1997	3.30595
1998	3.26404
1999	3.34766
2000	4.21327
2001	6.41901
2002	6.53395
2003	6.58622
2004	6.56655
2005	6.47919
2006	5.68791
2007	3.78336
2008	3.7961
2009	3.84852
2010	3.92448
2011	4.0044
2012	4.03658
2013	3.97281
2014	3.80492
2015	3.56065
2016	3.30807
2017	3.07244