Year	Percent
1965	23.14671
1966	22.62349
1967	23.52983
1968	24.14563
1969	25.23908
1970	25.70886
1971	23.56185
1972	22.67323
1973	26.05771
1974	29.43075
1975	23.50562
1976	26.29377
1977	24.1626
1978	23.61474
1979	24.1422
1980	26.46175
1981	24.4111
1982	23.46302
1983	21.99396
1984	23.04529
1985	22.90604
1986	21.49951
1987	21.87551
1988	22.32098
1989	22.0736
1990	22.30079
1991	21.94533
1992	21.32126
1993	18.85449
1994	18.79039
1995	19.81327
1996	19.13715
1997	19.26917
1998	19.48906
1999	20.00471
2000	20.71744
2001	20.66967
2002	21.41663
2003	21.06533
2004	21.17097
2005	21.10345
2006	21.89389
2007	22.18536
2008	21.7813
2009	19.39262
2010	20.5377
2011	20.46226
2012	17.86162
2013	16.95513
2014	17.033
2015	17.30646
2016	17.09498
2017	17.24968