Year	Percent
1960	11.53118
1961	12.30883
1962	12.71476
1963	12.70008
1964	12.34088
1965	11.94503
1966	12.0899
1967	11.49604
1968	10.77417
1969	9.92851
1970	9.01023
1971	7.9384
1972	7.32156
1973	6.92888
1974	6.78114
1975	6.94801
1976	7.59301
1977	7.35329
1978	7.06231
1979	6.69873
1980	6.34217
1981	5.9552
1982	5.40082
1983	5.12591
1984	5.17899
1985	5.26041
1986	5.44829
1987	5.66422
1988	4.84103
1989	2.82155
1990	0.14215
1991	-3.07904
1996	1.53401
1997	5.20015
1998	6.99905
1999	6.52545
2000	4.81497
2001	3.73105
2002	1.71337
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