Year	Percent
1960	4.75956
1961	4.42549
1962	4.10714
1963	3.8125
1964	3.55716
1965	3.33253
1966	3.11279
1967	2.91487
1968	2.82944
1969	2.87191
1970	3.0256
1971	3.21495
1972	3.37685
1973	3.47265
1974	3.48102
1975	3.42197
1976	3.34282
1977	3.27815
1978	3.24962
1979	3.26302
1980	3.10494
1981	1.9281
1982	1.97623
1983	1.94807
1984	1.83124
1985	1.65587
1986	1.45978
1987	1.28522
1988	1.14656
1989	1.06378
1990	1.01826
1991	0.99258
1992	0.95079
1993	0.89291
1994	0.80805
1995	0.70694
1996	0.6013
1997	0.5127
1998	0.47746
1999	0.50369
2000	0.49327
2001	0.01114
2002	0.08995
2003	0.14786
2004	0.16338
2005	0.15316
2006	0.13499
2007	0.12264
2008	0.12081
2009	0.12569
2010	0.14184
2011	0.1518
2012	0.2013
2013	0.23208
2014	0.24329
2015	0.23636
2016	0.22796
2017	0.22003