Year	Percent
1960	31.06755
1961	31.00028
1962	31.92283
1963	30.68922
1964	29.9218
1965	30.80013
1966	30.51143
1967	29.41949
1968	29.63463
1969	28.9824
1970	29.73917
1971	30.32413
1972	30.19885
1973	28.75061
1974	30.09027
1975	31.53621
1976	31.85986
1977	31.09245
1978	31.23525
1979	31.98778
1980	31.24807
1981	31.47761
1982	32.48422
1983	31.96138
1984	32.91523
1985	33.69993
1986	34.45945
1987	34.84594
1988	34.23597
1989	34.69057
1990	34.58723
1991	35.54965
1992	35.69122
1993	36.40126
1994	35.64104
1995	36.38569
1996	36.65073
1997	38.17392
1998	39.19719
1999	40.69436
2000	41.269
2001	42.57182
2002	43.53843
2003	43.66964
2004	42.84523
2005	42.89448
2006	42.73271
2007	42.47581
2008	44.84268
2009	45.53126
2010	45.17918
2011	45.44215
2012	46.30115
2013	46.69871
2014	47.82241
2015	47.91221
2016	47.87998
2017	48.93077