Year	Percent
1960	21.59269
1961	20.23989
1962	19.62127
1963	19.72245
1964	20.42682
1965	19.39357
1966	18.89965
1967	19.51468
1968	21.49628
1969	21.07225
1970	20.54891
1971	20.11998
1972	20.31829
1973	24.26863
1974	31.00596
1975	26.54833
1976	28.53265
1977	28.3698
1978	26.14426
1979	26.45378
1980	23.92525
1981	22.67417
1982	23.23608
1983	24.28367
1984	27.02553
1985	26.22814
1986	24.91395
1987	24.77039
1988	24.68539
1989	25.51461
1990	24.42114
1991	22.26511
1992	22.91416
1993	24.41729
1994	25.2914
1995	24.88595
1996	25.56817
1997	24.88946
1998	24.52824
1999	25.15867
2000	26.68715
2001	27.04261
2002	26.56884
2003	25.93693
2004	26.06865
2005	27.25388
2006	29.11738
2007	27.33929
2008	29.6665
2009	28.31591
2010	30.81987
2011	32.04973
2012	31.71203
2013	31.68405
2014	30.25244
2015	29.09516
2016	30.32709
2017	31.9332