Year	Percent
1965	20.30075
1966	20.65997
1967	20.10421
1968	19.49806
1969	19.43377
1970	18.63608
1971	19.23078
1972	18.85589
1973	18.61726
1974	17.87021
1975	18.24269
1976	18.96029
1977	18.39329
1978	15.95704
1979	20.64173
1980	23.47185
1981	27.61078
1982	30.24626
1983	33.12452
1984	34.64163
1985	34.31804
1986	32.48634
1987	29.05298
1988	28.32096
1989	28.96385
1990	28.75507
1991	28.8815
1992	25.10875
1993	28.4898
1994	29.01287
1995	25.78565
1996	26.47119
1997	26.41892
1998	26.55993
1999	27.49133
2000	29.91514
2001	26.13797
2002	26.91575
2003	26.8921
2004	26.71152
2005	28.09268
2006	29.70745
2007	28.64019
2008	29.69748
2009	27.03925
2010	27.17795
2011	27.19177
2012	28.1477
2013	27.6305
2014	27.13978
2015	25.18185
2016	24.48656
2017	24.0458