Year	Percent
1981	8.74066
1982	8.8333
1983	8.48349
1984	10.14246
1985	9.17406
1986	9.70419
1987	11.00483
1988	10.27592
1989	10.31786
1990	9.30387
1991	7.27711
1992	6.09402
1993	7.45467
1994	8.18346
1995	9.2862
1996	9.78369
1997	12.20217
1998	11.57038
1999	12.19479
2000	11.41047
2001	11.92793
2002	12.74028
2003	12.8995
2004	12.68554
2005	11.78883
2006	11.59232
2007	11.5895
2008	10.20685
2009	9.68348
2010	9.43513
2011	9.66464
2012	9.47614
2013	10.94456
2014	13.47132
2015	16.29779
2016	22.10148
2017	22.90242