Year	Percent
1971	12.85449
1972	12.66007
1973	18.20019
1974	16.48147
1975	17.08796
1976	15.42863
1977	16.58685
1978	12.62244
1979	17.61983
1980	13.40454
1981	11.87344
1982	6.56459
1983	6.68287
1984	8.13457
1985	9.68212
1986	10.18913
1987	4.75841
1988	6.41898
1989	4.11615
1990	1.5281
1991	9.74533
1992	10.72452
1993	13.27845
1994	5.93406
1995	8.22052
1996	8.08667
1997	9.19396
1998	11.33557
1999	14.58452
2000	13.68853
2001	21.1906
2002	7.21961
2003	3.84155
2004	10.56943
2005	24.89548
2006	24.67964
2007	28.32888
2008	25.3975
2009	30.20264
2010	28.70263
2011	27.25269
2012	16.10132
2013	19.62042
2014	18.51033
2015	19.75479
2016	21.88381