Year	Percent
1960	4.87936
1961	4.91501
1962	5.28513
1963	7.00097
1964	6.97928
1965	6.91244
1966	6.85582
1967	6.80782
1968	6.78568
1969	6.6662
1970	6.07745
1971	6.13607
1972	6.18198
1973	6.15612
1974	6.07843
1975	5.63981
1976	5.50754
1977	5.40134
1978	5.4144
1979	5.56131
1980	5.78452
1981	5.98477
1982	6.12824
1983	6.58181
1984	6.57797
1985	6.42971
1986	6.2821
1987	6.13255
1988	5.924
1989	5.66155
1990	5.37279
1991	5.07489
1992	4.79736
1993	3.50053
1994	3.1866
1995	3.07206
1996	2.9859
1997	2.89423
1998	2.79018
1999	2.66078
2000	2.52374
2001	2.38368
2002	2.28785
2003	0.7543
2004	0.59234
2005	0.72592
2006	0.87283
2007	1.01386
2008	1.1563
2009	1.29872
2010	1.42999
2011	1.56293
2012	1.67857
2013	1.75963
2014	1.88439
2015	1.97887
2016	2.06086
2017	2.14001