Year	Percent
1960	23.00787
1961	22.34314
1962	21.90486
1963	21.94234
1964	22.32288
1965	21.85658
1966	21.41812
1967	21.10609
1968	21.5646
1969	22.8423
1970	22.60094
1971	22.82435
1972	22.69311
1973	25.71017
1974	30.21629
1975	26.40675
1976	25.93325
1977	25.6942
1978	26.47823
1979	28.51774
1980	27.95924
1981	28.6532
1982	30.99821
1983	34.02897
1984	34.67426
1985	33.62001
1986	31.37102
1987	30.9732
1988	30.68888
1989	30.45511
1990	28.746
1991	26.86462
1992	26.72345
1993	31.30747
1994	34.49052
1995	38.00289
1996	36.83337
1997	40.05173
1998	41.02729
1999	41.03784
2000	44.09795
2001	43.75396
2002	42.09005
2003	41.24431
2004	43.44692
2005	45.87326
2006	48.19
2007	48.25807
2008	49.8131
2009	44.4523
2010	46.18519
2011	46.68289
2012	46.32314
2013	43.80069
2014	45.03315
2015	45.55123
2016	44.27323
2017	45.32459