Year	Percent
1971	3.09933
1972	9.97592
1973	11.15604
1974	16.48328
1975	5.15166
1976	10.73656
1977	15.4009
1978	14.83311
1979	22.57966
1980	32.49143
1981	27.45034
1982	18.15393
1983	16.21789
1984	17.89204
1985	16.31298
1986	12.26776
1987	13.50745
1988	11.69525
1989	11.28229
1990	12.39367
1991	13.02514
1992	13.05092
1993	13.9927
1994	12.35624
1995	11.98466
1996	15.03709
1997	12.82753
1998	15.58483
1999	18.01525
2000	20.3795
2001	21.1793
2002	24.94262
2003	26.98464
2004	26.3066
2005	24.43764
2006	31.3307
2007	38.51757
2008	32.7033
2009	36.85662
2010	48.52557
2011	50.1488
2012	44.66244
2013	37.44047
2014	38.18218
2015	34.36777
2016	36.77567