Year	Percent
1960	10.03018
1961	14.60475
1962	13.75503
1963	12.78045
1964	13.3028
1965	13.2117
1966	17.29472
1967	17.51425
1968	17.75034
1969	18.10927
1970	19.16034
1971	14.44467
1972	14.26297
1973	14.24786
1974	15.52616
1975	15.85952
1976	15.16374
1977	16.44499
1978	17.15104
1979	14.57538
1980	13.34276
1981	11.50527
1982	11.22469
1983	10.57055
1984	13.28297
1985	12.24165
1986	12.14856
1987	16.56455
1988	16.29924
1989	18.44881
1990	16.60215
1991	18.10963
1992	16.38378
1993	15.31752
1994	22.03227
1995	24.13448
1996	20.49243
1997	21.86614
1998	21.52058
1999	24.46542
2000	30.67932
2001	29.07857
2002	16.00838
2003	23.08574
2004	32.63644
2005	28.21239
2006	29.7285
2007	30.32365
2008	26.54134
2009	22.36939
2010	24.9741
2011	26.7428
2012	28.55778
2013	30.0643
2014	32.75823
2015	32.06401
2016	33.49672
2017	35.41856