Year	Percent
1970	29.5729
1971	28.00018
1972	22.75212
1973	20.88988
1974	16.81531
1975	15.39744
1976	16.25874
1977	19.7805
1978	21.69509
1979	21.83706
1980	28.18096
1981	25.74569
1982	28.25955
1983	22.66193
1984	37.72456
1985	35.10014
1986	23.77964
1987	35.21446
1988	44.7013
1989	38.98193
1990	29.92582
1991	30.98937
1992	48.39674
1993	30.85747
1994	21.7707
1995	22.30105
1996	23.05208
1997	23.99925
1998	11.367
1999	15.55015
2000	11.74095
2001	10.2246
2002	7.41547
2003	9.08279
2004	8.82455
2005	11.02634
2006	9.99073
2007	12.51998
2008	12.78604
2009	10.80213
2010	10.78524
2011	9.93499
2012	6.69904
2013	7.2244
2014	11.4166
2015	8.08555
2016	7.82309
2017	10.50571