Year	Percent
1960	15.8394
1961	15.78998
1962	15.70596
1963	15.66901
1964	11.51844
1965	11.37662
1966	11.64849
1967	13.92731
1968	15.28739
1969	16.53239
1970	16.14177
1971	19.93109
1972	21.289
1973	22.91954
1974	24.47292
1975	30.15112
1976	27.00824
1977	30.44327
1978	27.75083
1979	29.28244
1980	31.26251
1981	31.43511
1982	31.62404
1983	29.57415
1984	28.75779
1985	31.02608
1986	28.97117
1987	28.08113
1988	27.13098
1989	23.6459
1990	24.45596
1991	23.34869
1992	19.52754
1993	20.67354
1994	25.0276
1995	26.60691
1996	27.61669
1997	26.60389
1998	28.13168
1999	24.16796
2000	24.97978
2001	23.12583
2002	21.69622
2003	22.02231
2004	25.80014
2005	25.79172
2006	25.38254
2007	24.87483
2008	26.34324
2009	27.72151
2010	29.64009
2011	33.1503
2012	37.16053
2013	41.10186
2014	34.93506
2015	36.28741
2016	33.47224
2017	34.38478