Year	Percent
1970	13.76402
1971	14.12131
1972	14.30317
1973	13.0607
1974	12.97812
1975	14.31443
1976	14.42964
1977	12.88908
1978	12.21201
1979	12.03543
1980	11.24576
1981	11.77248
1982	13.6503
1983	14.29311
1984	15.74205
1985	17.05852
1986	18.38644
1987	19.54866
1988	20.47772
1989	25.53961
1990	26.71143
1991	32.33796
1992	31.35343
1993	33.61207
1994	30.71397
1995	26.69226
1996	24.47218
1997	23.12366
1998	23.85741
1999	22.21573
2000	22.12116
2001	20.95807
2002	20.95466
2003	19.9777
2004	17.79802
2005	15.09279
2006	17.47321
2007	17.06141
2008	19.2501
2009	19.47763
2010	17.72344
2011	18.50558
2012	21.7379
2013	23.30367
2014	22.74931
2015	22.94461
2016	20.40659