Year	Percent
1971	15.26277
1974	12.9422
1976	11.77488
1977	11.10739
1988	11.60536
1989	12.94889
1990	16.54902
1991	18.17415
1994	18.18517
1995	14.35593
1996	14.95249
1997	15.53102
1999	20.08695
2000	22.19265
2001	24.43856
2002	27.16888
2003	31.9948
2004	33.54591
2005	30.1514
2006	29.65744
2009	31.16352
2010	30.95984
2011	34.08097
2012	34.59373
2013	37.92018