Year	Percent
1970	38.00671
1971	27.95738
1972	24.74804
1973	19.25837
1974	15.70484
1990	21.87656
1991	21.24706
1992	17.38829
1993	16.23163
1994	17.15533
1995	14.01823
1996	13.52461
1997	22.04218
1998	18.43214
1999	20.88593
2000	18.86325
2001	20.80731
2002	27.23861
2003	19.64252
2004	15.37044
2005	14.15906
2006	13.04257
2007	12.22881
2008	13.16023
2009	14.73081
2010	16.65756
2011	14.10607
2012	10.65709
2013	10.86789
2014	9.76158
2015	10.1447
2016	13.95524