Year	Percent
1960	34.32181
1961	32.34234
1962	32.50493
1963	30.79128
1964	32.62801
1965	31.54015
1966	30.78321
1967	30.00146
1968	29.69673
1969	30.39418
1970	29.98376
1971	28.85012
1972	26.81466
1973	29.86687
1974	34.00511
1975	30.33013
1976	32.76949
1977	31.92512
1978	29.63467
1979	31.61479
1980	32.95299
1981	34.669
1982	34.96496
1983	33.71169
1984	34.61591
1985	35.65618
1986	32.49823
1987	29.64912
1988	30.13959
1989	31.62495
1990	30.86703
1991	31.464
1992	30.04754
1993	29.03876
1994	30.92865
1995	31.9026
1996	31.4039
1997	33.40558
1998	34.11257
1999	33.34877
2000	38.13667
2001	38.41407
2002	38.85246
2003	37.0433
2004	38.27932
2005	41.94765
2006	46.63667
2007	48.5853
2008	50.65241
2009	42.62898
2010	43.57704
2011	47.42562
2012	48.6105
2013	48.22133
2014	47.6508
2015	48.38336
2016	47.39003
2017	48.1519