Year	Percent
1960	32.68884
1961	31.03592
1962	30.18786
1963	30.69574
1964	30.88804
1965	29.76029
1966	29.35156
1967	29.04482
1968	32.87479
1969	33.37473
1970	31.60709
1971	31.02781
1972	30.3859
1973	35.40361
1974	44.81943
1975	40.02529
1976	43.46207
1977	45.25518
1978	42.78263
1979	42.36884
1980	39.94688
1981	37.90033
1982	38.17696
1983	39.15277
1984	43.03609
1985	42.96247
1986	38.80987
1987	38.33579
1988	36.75383
1989	37.76909
1990	37.3363
1991	34.55653
1992	34.88752
1993	36.81017
1994	38.50583
1995	37.83673
1996	38.74689
1997	37.8699
1998	36.32444
1999	35.84639
2000	38.44063
2001	38.02016
2002	36.43219
2003	34.58743
2004	34.10911
2005	36.10634
2006	39.49985
2007	35.1323
2008	39.09099
2009	36.67792
2010	41.25286
2011	45.17561
2012	43.87584
2013	43.82226
2014	39.55471
2015	37.65366
2016	39.45694
2017	41.52771