Year	Percent
1967	23.90371
1968	18.09512
1969	19.01222
1970	18.20153
1971	20.21576
1972	19.56931
1973	22.84323
1974	40.87015
1975	29.2644
1976	21.03115
1977	19.57941
1978	29.82857
1979	27.22604
1980	29.22374
1981	28.80289
1982	29.63334
1983	32.08272
1984	36.87897
1985	42.71817
1986	34.95817
1987	30.49478
1988	32.24621
1989	29.00523
1990	30.93057
1991	31.25571
1992	33.8729
1993	30.3921
1994	36.9915
1995	36.68316
1996	33.62294
1997	33.21086
1998	28.9244
1999	29.77545
2000	32.94398
2001	33.88837
2002	29.74184
2003	32.8588
2004	31.63443
2005	31.13646
2006	32.54773
2007	32.49764
2008	38.5202
2009	28.83396
2010	35.14813
2011	31.18738
2012	31.77805
2013	39.91209
2014	37.97016
2015	39.59421
2016	39.49635
2017	41.053