Year	Percent
1960	23.43322
1961	21.69139
1962	21.39248
1963	21.51853
1964	21.89269
1965	22.54388
1966	21.93692
1967	20.99227
1968	21.58395
1969	23.03915
1970	22.51219
1971	21.1605
1972	20.70027
1973	22.49304
1974	30.09612
1975	25.87383
1976	26.76828
1977	26.52025
1978	24.82414
1979	28.66705
1980	28.93714
1981	28.11994
1982	30.77652
1983	31.47228
1984	30.7152
1985	31.56788
1986	27.96782
1987	28.80627
1988	28.75196
1989	29.67718
1990	28.11081
1991	25.18285
1992	25.00106
1993	27.93313
1994	30.43631
1995	31.62423
1996	30.6554
1997	33.10256
1998	34.71656
1999	34.97154
2000	38.22946
2001	37.52224
2002	35.77352
2003	34.90382
2004	35.84691
2005	38.70071
2006	40.59949
2007	41.28171
2008	43.54603
2009	38.691
2010	40.71765
2011	41.97863
2012	41.39188
2013	39.29299
2014	40.7175
2015	40.68957
2016	39.43439
2017	41.11748