Year	Percent
1968	24.71526
1969	24.94258
1970	21.56377
1971	17.9173
1972	18.27192
1973	20.91546
1974	13.20216
1975	21.73281
1976	24.25157
1977	32.56106
1978	41.59768
1979	34.24394
1980	27.30036
1981	30.09319
1982	39.11835
1983	47.67661
1984	45.22248
1985	36.64241
1986	35.78629
1987	37.13259
1988	35.20282
1989	38.07738
1990	31.37322
1991	36.39089
1992	35.98522
1993	33.45417
1994	26.07037
1995	27.7039
1996	26.63101
1997	26.02949
1998	26.45601
1999	23.17959
2000	24.76118
2001	23.92691
2002	23.64399
2003	23.97703
2004	24.09751
2005	24.90333
2006	30.1127
2007	34.92588
2008	33.99113
2009	37.76972
2010	32.98004
2011	29.49428
2012	29.24096
2013	30.79109
2014	33.76518
2015	38.75382
2016	30.71782
2017	28.13666