Year	Percent
1971	5.22944
1972	7.95158
1973	12.92519
1974	13.44382
1975	9.78635
1976	10.0574
1977	9.46178
1978	9.55593
1979	12.82726
1980	15.78633
1981	13.75443
1982	15.48853
1983	22.30834
1984	13.1701
1985	10.61603
1986	9.79557
1987	8.57759
1988	6.98906
1989	7.09741
1990	5.06417
1991	5.22097
1992	6.11525
1993	8.12929
1994	13.56997
1995	8.3614
1996	4.38239
1997	5.96608
1998	5.03567
1999	6.20179
2000	6.32063
2001	13.21688
2002	26.01774
2003	32.4032
2004	29.50093
2005	32.6574
2006	34.64218
2007	37.60904
2008	18.22167
2009	24.15013
2010	27.47654
2011	27.45188
2012	22.05454
2013	13.21884
2014	23.39753
2015	30.45721
2016	30.30037