Year	Percent
1960	4.39346
1961	3.80546
1962	3.62308
1963	3.59246
1964	3.56585
1965	3.53988
1966	3.51939
1967	3.4921
1968	3.44356
1969	3.36122
1970	3.26692
1971	3.17135
1972	3.09567
1973	3.05295
1974	3.04944
1975	3.08053
1976	3.11358
1977	2.66362
1978	2.39279
1979	2.44314
1980	2.49584
1981	2.53866
1982	2.57625
1983	2.62227
1984	2.67882
1985	2.73363
1986	2.79207
1987	2.61164
1988	2.44916
1989	2.33559
1990	2.17337
1991	2.0011
1992	1.85317
1993	1.73625
1994	1.66246
1995	1.62335
1996	1.58413
1997	1.80398
1998	1.94554
1999	1.94384
2000	1.9569
2001	1.97941
2002	2.00308
2003	2.00642
2004	1.9817
2005	1.94226
2006	1.88943
2007	1.75957
2008	1.71897
2009	1.80533
2010	1.9258
2011	2.06167
2012	2.08004
2013	2.12204
2014	2.08217
2015	1.99216
2016	1.89284
2017	1.86653