Year	Percent
1960	25.37023
1961	24.08005
1962	24.6171
1963	25.95414
1964	26.81756
1965	26.09872
1966	24.88206
1967	24.3568
1968	24.16645
1969	23.91575
1970	23.81417
1971	23.12949
1972	22.11405
1973	26.60282
1974	25.89542
1975	23.31026
1976	24.23925
1977	24.39633
1978	25.34222
1979	27.36423
1980	29.61369
1981	27.00577
1982	24.79175
1983	23.48824
1984	25.37861
1985	26.912
1986	26.74672
1987	29.59091
1988	29.41367
1989	27.41502
1990	26.29569
1991	25.66463
1992	26.66569
1993	28.34408
1994	31.33227
1995	31.15166
1996	31.40823
1997	29.63909
1998	30.2139
1999	32.24499
2000	32.62357
2001	33.65149
2002	34.91182
2003	34.19756
2004	32.02274
2005	33.40517
2006	35.23577
2007	35.99856
2008	36.81696
2009	34.51915
2010	36.20445
2011	36.96773
2012	33.53708
2013	31.46229
2014	32.54221
2015	29.39095
2016	32.15703
2017	34.71377