Year	Percent
1960	7.35444
1961	7.36189
1962	7.3733
1963	7.38708
1964	7.40324
1965	7.39792
1966	7.40602
1967	7.41679
1968	7.41885
1969	7.40568
1970	7.40598
1971	7.38301
1972	7.37253
1973	6.63701
1974	4.42314
1975	4.50049
1976	4.56379
1977	4.60731
1978	4.62915
1979	4.61935
1980	4.58673
1981	4.55206
1982	4.53379
1983	5.9894
1984	8.04212
1985	7.87354
1986	7.67985
1987	7.51378
1988	7.46265
1989	7.5255
1990	7.67702
1991	7.8453
1992	7.93906
1993	7.01234
1994	3.70125
1995	3.34749
1996	2.9563
1997	2.65142
1998	2.47098
1999	2.45474
2000	2.55295
2001	2.6795
2002	2.75734
2003	2.7656
2004	2.67948
2005	2.53712
2006	2.38555
2007	2.27594
2008	2.22433
2009	2.31188
2010	2.45224
2011	2.60285
2012	2.73065
2013	2.84235
2014	2.92289
2015	2.98913
2016	3.04795
2017	3.11014