Year	Percent
1960	10.29781
1961	11.12198
1962	11.56953
1963	11.59631
1964	11.27576
1965	10.7624
1966	10.2858
1967	9.81906
1968	9.21482
1969	8.48637
1970	7.74267
1971	7.0285
1972	6.46
1973	6.11787
1974	6.01392
1975	6.04333
1976	6.08177
1977	6.04072
1978	5.92029
1979	5.70585
1980	5.43809
1981	5.02168
1982	4.62614
1983	4.48491
1984	4.64756
1985	4.90026
1986	5.43397
1987	5.64889
1988	4.82677
1989	2.80722
1990	0.12787
1991	-3.09334
1996	1.30085
1997	4.99492
1998	6.81854
1999	6.36649
2000	4.67548
2001	2.8181
2002	1.62131
2003	1.17253
2004	1.77389
2005	3.06337
2006	4.32545
2007	5.17061
2008	5.77885
2009	6.09183
2010	6.16125
2011	6.23772
2012	6.21172
2013	5.80176
2014	4.98868
2015	3.97407
2016	2.92421
2017	2.05021