Year	Percent
1968	27.62963
1969	24.45071
1970	60.51622
1971	67.04373
1972	69.53105
1973	72.31996
1974	85.03242
1975	73.33854
1976	69.09298
1977	62.48861
1978	55.61382
1979	56.21938
1980	65.64148
1981	21.15912
1982	25.85346
1983	34.35046
1984	32.8287
1985	21.45313
1986	19.45935
1987	17.71814
1988	19.68843
1989	19.44492
1990	15.68423
1991	19.98562
1992	22.96365
1993	25.05498
1994	20.35695
1995	20.28614
1996	18.57124
1997	18.77753
1998	22.94931
1999	21.51362
2000	19.317
2001	19.6231
2002	19.69335
2003	19.49249
2004	19.86462
2005	20.17483
2006	22.21516
2007	26.47285
2008	27.29579
2009	31.71528
2010	30.92629
2011	26.97085
2012	26.54156
2013	26.46973
2014	28.75059
2015	35.08346
2016	30.93262
2017	28.2416