Year	Percent
1965	26.38655
1966	24.66219
1967	25.63819
1968	25.3486
1969	23.18658
1970	24.83494
1971	24.63157
1972	29.09505
1973	29.96006
1974	32.4177
1975	33.04673
1976	35.54383
1977	38.1651
1978	30.26637
1979	36.97151
1980	34.16155
1981	26.67869
1982	22.7774
1983	24.48852
1984	21.75414
1985	22.32377
1986	24.66816
1987	18.9923
1988	15.81068
1989	13.23779
1990	18.49699
1991	17.22577
1992	16.13292
1993	19.3723
1994	19.92272
1995	21.5545
1996	21.14099
1997	26.02184
1998	24.38659
1999	24.3964
2000	26.82727
2001	25.00929
2002	25.51309
2003	25.92342
2004	25.90621
2005	25.26653
2006	25.9397
2007	25.56703
2008	26.74059
2009	23.95121
2010	26.94667
2011	28.98177
2012	28.53061
2013	29.21956
2014	28.94434
2015	28.99953
2016	27.86503
2017	27.63784