Year	Percent
1960	20.35746
1961	18.68802
1962	17.85678
1963	18.39489
1964	17.86747
1965	19.22876
1966	19.26378
1967	18.40378
1968	18.7683
1969	19.06431
1970	19.79369
1971	18.91868
1972	19.06026
1973	22.07269
1974	25.3039
1975	26.82211
1976	27.66939
1977	26.56379
1978	25.29137
1979	24.77639
1980	27.62818
1981	24.94149
1982	26.22579
1983	28.14752
1984	29.6772
1985	30.68327
1986	30.14921
1987	30.00788
1988	23.27787
1989	29.93089
1990	28.48267
1991	28.76647
1992	28.16097
1993	27.9894
1994	26.50988
1995	26.99623
1996	27.38829
1997	26.71531
1998	28.49863
1999	29.18361
2000	34.75687
2001	32.6936
2002	27.29258
2003	28.8395
2004	28.29999
2005	28.94242
2006	30.86811
2007	32.05988
2008	33.56124
2009	27.24766
2010	31.6886
2011	35.1964
2012	40.20461
2013	41.13526
2014	42.28665
2015	39.4202
2016	39.9645
2017	44.65853