Year	Percent
1960	32.91264
1961	28.48543
1962	29.2013
1963	27.49257
1964	26.72174
1965	25.4948
1966	25.84863
1967	23.30419
1968	23.58869
1969	24.61736
1970	28.6007
1971	26.6121
1972	23.89978
1973	25.55966
1974	33.89845
1975	34.9588
1976	31.38099
1977	30.15629
1978	39.54529
1979	45.75372
1980	54.7988
1981	46.53609
1982	46.25748
1983	41.4314
1984	34.74367
1985	37.9652
1986	35.32935
1987	35.69639
1988	36.83677
1989	36.75677
1990	38.06311
1991	38.85483
1992	41.03338
1993	43.34651
1994	45.61791
1995	46.03742
1996	43.90063
1997	43.59944
1998	42.25117
1999	43.26777
2000	49.62074
2001	43.56741
2002	41.4218
2003	40.68274
2004	44.15204
2005	41.2671
2006	41.13265
2007	39.49151
2008	38.52756
2009	27.82078
2010	26.81157
2011	34.08774
2012	31.6756
2013	28.93739
2014	29.16212
2015	28.54569
2016	28.67564
2017	29.13978