Year	Percent
1960	22.24075
1961	21.38176
1962	21.43795
1963	19.40763
1964	21.19876
1965	21.0452
1966	20.63142
1967	19.78902
1968	20.2324
1969	22.27883
1970	25.53235
1971	24.85589
1972	24.11928
1973	24.885
1974	29.51209
1975	28.17803
1976	25.70196
1977	25.51973
1978	24.74723
1979	28.51377
1980	32.10023
1981	30.28823
1982	28.6825
1983	28.6922
1984	27.09447
1985	27.30033
1986	24.31782
1987	24.46754
1988	24.24238
1989	24.84028
1990	23.68201
1991	22.2028
1992	24.67708
1993	26.77147
1994	28.38666
1995	28.30675
1996	29.40917
1997	30.46289
1998	29.55093
1999	28.6339
2000	32.90743
2001	30.55311
2002	30.20453
2003	30.77146
2004	32.40218
2005	36.3721
2006	39.0119
2007	39.17914
2008	41.43389
2009	34.26026
2010	37.41208
2011	40.01036
2012	40.92436
2013	39.69942
2014	38.15227
2015	36.9659
2016	36.77476
2017	38.12869