Year	Percent
1971	8.68549
1973	15.11752
1974	14.68415
1975	15.44715
1976	14.17021
1977	14.64641
1978	14.46277
1979	14.44942
1980	14.75291
1981	15.29363
1982	18.23672
1983	25.00775
1984	34.55043
1985	36.76005
1986	37.59161
1987	37.21903
1988	50.11347
1989	40.83894
1990	49.69082
1991	50.05759
1992	56.52692
1993	60.16431
2000	27.33781
2001	28.25747
2002	29.11141
2003	35.33435
2004	39.44367
2005	39.95691
2007	43.46962
2008	46.09993
2009	51.48
2010	54.05463
2011	57.73721
2012	63.19696
2013	69.62492
2014	67.32331
2015	62.09666
2016	64.97652