Year	Percent
1960	2.57879
1961	4.67514
1962	4.83736
1963	4.96716
1964	5.15135
1965	5.21716
1966	5.2603
1967	5.35515
1968	5.28635
1969	5.02087
1970	4.96489
1971	4.8469
1972	4.73427
1973	4.52024
1974	4.22268
1975	4.05157
1976	3.70502
1977	3.52705
1978	3.67096
1979	4.21749
1980	5.29354
1981	8.35415
1982	8.9276
1983	9.33519
1984	9.62842
1985	9.54366
1986	9.70326
1987	9.49346
1988	9.35633
1989	8.76446
1990	8.04176
1991	6.76962
1992	3.07489
1993	2.72849
1994	2.61462
1995	2.73617
1996	2.84618
1997	2.95765
1998	2.98343
1999	2.99253
2000	2.89398
2001	2.76747
2002	2.74782
2003	2.83446
2004	3.11885
2005	3.44494
2006	3.84097
2007	4.11488
2008	4.20021
2009	3.97139
2010	3.64769
2011	3.21021
2012	2.92551
2013	2.67737
2014	2.59293
2015	2.55591
2016	2.59645
2017	2.53751