Year	Percent
1980	23.11559
1981	22.98264
1982	19.375
1983	18.1966
1984	17.41308
1985	16.23555
1986	15.0575
1987	15.4663
1988	16.38229
1989	17.94015
1990	14.86945
1991	7.22458
1992	11.49044
1993	15.42252
1994	11.35169
1995	12.47537
1996	11.19577
1997	9.74565
1998	10.8443
1999	15.81673
2000	17.86708
2001	18.43157
2002	19.59887
2003	20.35591
2004	21.98294
2005	22.82407
2006	24.934
2007	28.08422
2008	25.3024
2009	25.24074
2010	27.97947
2011	29.2415
2012	28.93749
2013	28.91635
2014	28.21298
2015	27.26738
2016	28.92342
2017	31.52204