Year	Percent
1960	2.44272
1961	2.34335
1962	2.26344
1963	2.23421
1964	2.26672
1965	2.34554
1966	2.43147
1967	2.50316
1968	2.58877
1969	2.67578
1970	2.76164
1971	2.84781
1972	2.92769
1973	2.98961
1974	3.02653
1975	3.04618
1976	3.08335
1977	3.121
1978	3.12119
1979	3.0855
1980	3.03342
1981	2.92415
1982	2.84998
1983	2.94159
1984	3.23664
1985	3.62609
1986	4.05217
1987	4.32647
1988	4.30768
1989	3.94703
1990	3.38758
1991	2.77637
1992	2.27855
1993	1.96623
1994	1.90262
1995	1.99926
1996	2.1593
1997	2.23914
1998	2.16895
1999	1.89421
2000	1.50342
2001	1.07376
2002	0.74314
2003	0.59604
2004	0.70206
2005	0.98323
2006	1.31524
2007	1.58661
2008	1.78151
2009	1.86176
2010	1.86016
2011	1.84635
2012	1.85174
2013	1.84938
2014	1.84229
2015	1.82966
2016	1.80967
2017	1.78255