Year	Percent
1970	37.40867
1971	31.30482
1972	29.84264
1973	28.05899
1974	16.03707
1975	27.223
1976	28.65644
1977	31.77831
1978	38.24686
1979	33.89654
1980	27.51896
1981	28.2375
1982	38.60807
1983	48.41811
1984	51.14489
1985	54.89742
1986	57.25406
1987	54.1546
1988	55.12545
1989	51.25309
1990	45.13649
1991	45.73188
1992	42.8275
1993	45.98712
1994	46.0382
1995	44.94694
1996	42.42587
1997	43.80736
1998	49.89284
1999	46.6937
2000	40.9122
2001	43.30376
2002	43.18047
2003	40.87688
2004	38.92398
2005	34.66439
2006	34.17436
2007	34.19514
2008	30.92646
2009	42.12591
2010	38.97556
2011	34.15221
2012	35.2295
2013	37.98022
2014	40.59719
2015	52.10816
2016	54.15691
2017	52.46021