Year	Percent
1960	18.0013
1961	18.78997
1962	13.49473
1963	12.56653
1964	12.69571
1965	12.35427
1966	11.96111
1967	10.85584
1968	11.84619
1969	12.21606
1970	13.20179
1971	13.42358
1972	14.9883
1973	16.64752
1974	21.03846
1975	17.9954
1976	15.62373
1977	14.40473
1978	13.80123
1979	15.579
1980	19.1865
1981	17.97382
1982	14.64203
1983	19.03548
1984	20.19625
1985	17.92881
1986	14.13679
1987	14.55536
1988	14.99679
1989	12.74873
1990	11.67611
1991	9.05185
1992	14.69324
1993	15.14281
1994	14.25198
1995	13.08237
1996	12.29259
1997	13.16631
1998	12.99893
1999	16.6703
2000	17.41459
2001	20.89188
2002	21.67056
2003	22.19928
2004	24.36981
2005	21.99979
2006	21.09393
2007	20.56384
2008	22.42681
2009	17.19666
2010	17.81235
2011	18.84425
2012	19.30791
2013	19.92025
2014	18.90301
2015	20.52844
2016	18.32667
2017	18.25559