Year	Percent
1960	8.61959
1961	8.77573
1962	8.94408
1963	8.46506
1964	7.71687
1965	7.20695
1966	8.07084
1967	9.06337
1968	8.87311
1969	8.27294
1970	7.6897
1971	6.64348
1972	6.27183
1973	5.66875
1974	5.72917
1975	5.39791
1976	4.98816
1977	4.97138
1978	4.76281
1979	4.77242
1980	4.95637
1981	5.4332
1982	6.56668
1983	6.04385
1984	5.88815
1985	6.12131
1986	6.30273
1987	6.08395
1988	5.74644
1989	5.54685
1990	5.27832
1991	4.57218
1992	4.66626
1993	4.32694
1994	3.94128
1995	3.63847
1996	3.35074
1997	3.20991
1998	3.01763
1999	2.9084
2000	2.93343
2001	2.94435
2002	3.24956
2003	3.60728
2004	3.78558
2005	3.84424
2006	3.8082
2007	3.84705
2008	4.22004
2009	4.6368
2010	4.66561
2011	4.58398
2012	4.23873
2013	3.83251
2014	3.4997
2015	3.28963
2016	3.22213
2017	3.14922