Year	Percent
1971	20.9709
1972	20.62927
1973	30.99429
1974	33.73468
1975	22.75016
1976	8.47519
1977	19.22717
1978	12.94335
1979	11.3727
1980	9.15017
1981	6.59204
1982	3.29853
1983	2.27449
1984	6.88182
1985	4.81433
1986	2.5595
1987	4.24684
1988	11.09891
1989	7.47884
1990	9.11944
1991	9.47432
1992	2.58805
1993	3.38897
1994	2.36097
1995	5.13547
1996	9.74517
1997	6.55588
1998	10.62514
1999	9.07312
2000	9.07551
2001	7.95056
2002	5.71799
2003	4.09466
2004	3.88178
2005	5.16993
2006	16.30294
2007	26.16444
2008	25.5281
2009	14.2687
2010	31.87713
2011	17.88553
2012	18.40428
2013	27.46691
2014	37.26106
2015	39.13293