Year	Percent
1975	41.3299
1976	26.93581
1977	33.86603
1978	28.78943
1979	26.07816
1980	30.06222
1981	25.37526
1982	27.58812
1983	18.65777
1984	26.60802
1985	30.12861
1986	25.71235
1987	30.92672
1988	22.73656
1989	25.1033
1990	33.87018
1991	22.9033
1992	23.64197
1993	19.89409
1994	17.38155
1995	17.48874
1996	20.35009
1997	21.13908
1998	19.88051
1999	15.63358
2000	14.44389
2001	13.03831
2002	18.25897
2003	19.35961
2004	19.67719
2005	17.81745
2006	14.46606
2007	12.15362
2008	15.72573
2009	13.37492
2010	12.41294
2011	15.91182
2012	17.01204
2013	20.35297
2014	16.816
2015	17.02144
2016	21.31334