Year	Percent
1960	8.51994
1961	8.65423
1962	8.7078
1963	8.80124
1964	9.63911
1965	8.71195
1966	7.97208
1967	8.02272
1968	8.27018
1969	9.61031
1970	10.27003
1971	14.8739
1972	17.27749
1973	20.63107
1974	25.52317
1975	23.10422
1976	22.8445
1977	19.56245
1978	18.31893
1979	16.40009
1980	15.10695
1981	14.13093
1982	17.92663
1983	17.13227
1984	14.16663
1985	22.95328
1986	20.13659
1987	19.22266
1988	18.78891
1989	20.41002
1990	18.9134
1991	21.24561
1992	19.30243
1993	19.4594
1994	27.16616
1995	23.92534
1996	24.94471
1997	27.39178
1998	24.17456
1999	18.30478
2000	20.06839
2001	13.78887
2002	17.53587
2003	21.30612
2004	21.66315
2005	24.09578
2006	20.70577
2007	22.24628
2008	25.4125
2009	24.87155
2010	26.93086
2011	27.96709
2012	32.45217
2013	32.50006
2014	25.8521
2015	24.32829
2016	23.15824
2017	25.53614