Year	Percent
1960	14.53622
1961	13.49494
1962	13.42253
1963	15.93285
1964	18.08945
1965	19.61094
1966	19.13425
1967	19.51152
1968	18.41664
1969	17.43034
1970	17.77836
1971	18.6971
1972	18.53614
1973	20.20473
1974	25.66503
1975	23.53328
1976	27.58344
1977	26.25673
1978	27.26254
1979	25.85113
1980	24.91909
1981	23.60151
1982	18.68762
1983	14.55248
1984	15.151
1985	12.98402
1986	14.59212
1987	22.29406
1988	21.93624
1989	22.4741
1990	24.84196
1991	21.56765
1992	27.29626
1993	26.0759
1994	24.85095
1995	25.43039
1996	22.58284
1997	23.59584
1998	26.25213
1999	27.35558
2000	28.95055
2001	41.33709
2002	39.73291
2003	40.18598
2004	42.10262
2005	40.99397
2006	41.88646
2007	42.33323
2008	39.40704
2009	33.13061
2010	36.30927
2011	37.35863
2012	36.11393
2013	34.82866
2014	33.5595
2015	30.14582
2016	27.46278
2017	26.86122