Year	Percent
1960	20.77695
1961	20.97284
1962	21.3084
1963	21.91065
1964	20.91953
1965	21.44218
1966	22.57665
1967	22.84443
1968	23.2771
1969	24.92494
1970	24.93265
1971	25.00694
1972	26.19648
1973	28.59945
1974	35.97374
1975	32.39255
1976	36.24026
1977	36.37703
1978	35.8532
1979	38.26101
1980	37.59756
1981	39.91105
1982	37.83445
1983	34.5769
1984	36.5972
1985	36.4765
1986	30.79869
1987	30.18123
1988	29.97858
1989	31.71647
1990	29.92136
1991	28.35048
1992	27.86169
1993	29.89547
1994	32.90718
1995	37.56071
1996	35.1857
1997	36.36219
1998	36.66292
1999	36.53804
2000	41.97681
2001	41.35787
2002	39.59238
2003	38.02456
2004	39.43039
2005	40.91005
2006	44.24046
2007	45.91554
2008	46.2063
2009	37.61802
2010	43.96819
2011	47.53544
2012	47.75639
2013	46.83029
2014	46.66437
2015	47.38417
2016	46.72515
2017	49.55817