Year	Percent
1980	17.07477
1981	21.46914
1982	22.92743
1983	24.62795
1984	22.77306
1985	22.63848
1986	17.60986
1987	18.09904
1988	16.70766
1989	19.22545
1990	17.13197
1991	16.56407
1992	17.28301
1993	13.26083
1994	15.0463
1995	17.13695
1996	20.19916
1997	27.44173
1998	22.79615
1999	20.97595
2000	27.00722
2001	29.80941
2002	32.54496
2003	31.36435
2004	32.00417
2005	37.77736
2006	45.13221
2007	36.01741
2008	36.89596
2009	31.07745
2010	32.67032
2011	35.51924
2012	40.4318
2013	40.49244
2014	40.36114
2015	44.90744
2016	38.48138
2017	39.1275