Year	Percent
1960	5.85958
1961	8.72363
1962	10.68118
1963	11.01272
1964	9.82482
1965	8.1966
1966	6.51298
1967	5.92862
1968	7.30839
1969	10.66916
1970	14.44694
1971	16.88167
1972	17.68981
1973	17.6953
1974	17.12561
1975	16.21187
1976	15.45088
1977	14.53012
1978	13.03346
1979	11.07131
1980	9.06586
1981	7.26215
1982	5.94389
1983	5.20177
1984	5.08895
1985	5.35823
1986	5.67098
1987	5.83759
1988	5.91679
1989	5.87491
1990	5.7607
1991	5.73767
1992	5.75079
1993	5.6263
1994	5.34865
1995	5.03021
1996	4.86964
1997	4.89528
1998	4.98952
1999	5.15078
2000	5.43062
2001	5.28153
2002	5.30471
2003	6.47749
2004	8.84369
2005	11.35644
2006	13.51058
2007	14.23679
2008	13.16147
2009	10.61544
2010	7.5871
2011	4.7437
2012	2.5948
2013	1.1818
2014	0.71476
2015	0.91561
2016	1.25176
2017	1.39836