Year	Percent
1960	9.43038
1961	9.07944
1962	8.88869
1963	9.01976
1964	9.61687
1965	10.42693
1966	11.3221
1967	11.94728
1968	12.10906
1969	11.68845
1970	9.59977
1971	4.76362
1972	4.29591
1973	3.94004
1974	3.77151
1975	3.73472
1976	3.69219
1977	3.6354
1978	3.73184
1979	3.99404
1980	4.35833
1981	4.734
1982	5.07016
1983	5.25555
1984	5.20321
1985	5.01829
1986	4.84341
1987	4.69939
1988	4.53006
1989	4.33274
1990	4.14669
1991	3.93087
1992	3.75592
1993	3.70653
1994	3.81995
1995	4.02685
1996	4.26836
1997	4.44587
1998	4.52016
1999	4.46404
2000	4.32138
2001	4.16041
2002	4.0452
2003	3.96946
2004	3.95202
2005	3.96962
2006	3.99272
2007	3.99862
2008	4.00014
2009	3.97978
2010	3.96179
2011	3.99618
2012	4.00457
2013	3.96671
2014	3.92361
2015	3.87369
2016	3.83197
2017	3.78994