Year	Percent
1960	11.47515
1961	14.02489
1962	19.23466
1963	16.95382
1964	18.49113
1965	18.95919
1966	18.30131
1967	20.60486
1968	19.49053
1969	17.77569
1970	21.0449
1971	20.41429
1972	19.46931
1973	19.88902
1974	27.35261
1975	27.10977
1976	25.2486
1977	24.12565
1978	24.93707
1979	26.63677
1980	28.47109
1981	27.17155
1982	26.13588
1983	28.08113
1984	25.07317
1985	21.89346
1986	22.37443
1987	26.22136
1988	26.93905
1989	30.2685
1990	33.28404
1991	32.58769
1992	34.02819
1993	39.80686
1994	40.13386
1995	44.18125
1996	49.2933
1997	59.29384
1998	53.89801
1999	49.42015
2000	53.36056
2001	52.88209
2002	55.68807
2003	54.69228
2004	54.06987
2005	51.74157
2006	48.36277
2007	43.35861
2008	39.37023
2009	33.35803
2010	36.6162
2011	35.66707
2012	34.0804
2013	32.22761
2014	32.55891
2015	34.29429
2016	36.93584
2017	40.10539