Year	Percent
1960	13.7931
1961	14.20455
1962	11.34021
1963	12.01717
1964	11.9403
1965	18.39709
1966	17.12821
1967	14.60942
1968	15.18268
1969	13.39771
1970	13.88679
1971	10.2844
1972	15.43624
1973	10.41789
1974	14.38207
1975	16.78043
1976	19.5594
1977	19.89644
1978	18.84697
1979	16.8331
1980	15.03297
1981	15.20411
1982	14.32587
1983	25.68887
1984	26.58062
1985	26.75653
1986	26.21509
1987	21.6487
1988	22.05789
1989	23.49387
1990	23.53212
1991	20.69367
1992	20.44757
1993	19.12602
1994	19.76681
1995	18.99681
1996	19.66998
1997	17.45785
1998	16.41991
1999	15.09765
2000	16.6981
2001	16.80466
2002	20.62167
2003	27.43242
2004	32.1123
2005	30.40402
2006	30.2975
2007	29.09049
2008	30.20302
2009	27.09922
2010	26.34299
2011	26.42215
2012	25.91963
2013	23.35314
2014	23.54266
2015	22.47785
2016	21.42754
2017	21.55827