Year	Percent
1960	3.26296
1961	3.31644
1962	3.1945
1963	3.22343
1964	3.2106
1965	3.16849
1966	3.11462
1967	3.05423
1968	3.0016
1969	2.95113
1970	2.90745
1971	2.8642
1972	3.79154
1973	3.70625
1974	3.6143
1975	3.51067
1976	3.41032
1977	3.30549
1978	3.19289
1979	3.05857
1980	2.9184
1981	2.7733
1982	2.64778
1983	2.54639
1984	2.48851
1985	2.44945
1986	2.41679
1987	2.38361
1988	2.36817
1989	2.37091
1990	2.38345
1991	2.40449
1992	2.41452
1993	3.5215
1994	3.75995
1995	3.59332
1996	3.42115
1997	3.24962
1998	3.09495
1999	1.76018
2000	1.67247
2001	1.58384
2002	1.50045
2003	1.43172
2004	1.38601
2005	1.35003
2006	1.32589
2007	1.38427
2008	1.86979
2009	1.83158
2010	1.80136
2011	1.77709
2012	1.75347
2013	1.72927
2014	1.70952
2015	1.68906
2016	1.65215
2017	1.61271