Year	Percent
1965	19.21968
1966	19.26807
1967	20.19298
1968	20.26031
1969	21.47076
1970	20.57967
1971	20.50613
1972	20.05621
1973	21.32372
1974	27.09652
1975	25.92741
1976	25.16296
1977	25.74935
1978	26.36982
1979	28.89459
1980	31.11142
1981	32.01586
1982	31.0507
1983	32.50119
1984	33.50228
1985	32.74012
1986	30.48293
1987	29.47245
1988	30.60065
1989	31.13901
1990	29.78818
1991	28.97712
1992	28.45803
1993	28.08907
1994	29.21815
1995	29.39514
1996	28.48848
1997	26.50087
1998	25.77545
1999	26.0459
2000	26.65247
2001	26.51032
2002	26.55936
2003	25.26284
2004	25.49062
2005	26.60147
2006	26.70698
2007	28.66931
2008	31.45267
2009	27.76956
2010	28.97874
2011	29.80671
2012	29.63752
2013	28.75662
2014	26.90048
2015	25.20004
2016	24.43189