Year	Percent
1960	4.49376
1961	3.52657
1962	3.54015
1963	3.5527
1964	3.55387
1965	3.55355
1966	3.53874
1967	3.5222
1968	3.49961
1969	3.47729
1970	3.97423
1971	5.4989
1972	5.44508
1973	5.35504
1974	5.24662
1975	5.10507
1976	4.97715
1977	4.83716
1978	4.71794
1979	4.6071
1980	4.14527
1981	2.94792
1982	2.85878
1983	2.79865
1984	2.7697
1985	2.75035
1986	2.76077
1987	2.74697
1988	2.67658
1989	2.52484
1990	2.2792
1991	1.75962
1992	1.57977
1993	1.47995
1994	1.48512
1995	1.56329
1996	1.67255
1997	1.74334
1998	1.76176
1999	1.70848
2000	2.37752
2001	4.56077
2002	4.4094
2003	4.26459
2004	4.14462
2005	4.02524
2006	3.92523
2007	3.81142
2008	3.71041
2009	3.60963
2010	3.52726
2011	2.37868
2012	2.12108
2013	2.07242
2014	2.01144
2015	1.93854
2016	1.86801
2017	1.79261