Year	Percent
1983	8.0777
1984	8.0254
1985	7.3584
1986	7.1413
1987	7.2855
1988	6.945
1989	5.3003
1990	4.5548
1991	4.552
1992	4.7921
1993	6.16
1994	7.6981
1995	7.3103
1996	7.4062
1997	7.0891
1998	7.5815
1999	7.4724
2000	5.306
2001	5.6293
2002	6.243
2003	7.4405
2004	6.6489
2005	7.5967
2006	7.3963
2007	6.6617
2008	6.4679
2009	7.7447
2010	8.1073
2011	7.1061
2012	7.6516
2013	8.6404
2014	9.0203
2015	9.0935
2016	8.0596
2017	7.1138