Year	Percent
1981	14.037
1982	18.12603
1983	18.83242
1984	21.87652
1985	28.91254
1986	37.46406
1987	37.17783
1988	40.43943
1989	38.69402
1990	33.48282
1991	34.38242
1992	32.77153
1993	33.86706
1994	30.96484
1995	30.27615
1996	37.14854
1997	30.32378
1998	32.26219
1999	30.62329
2000	22.84671
2001	23.9561
2002	25.22353
2003	26.32201
2004	25.46585
2005	20.90497
2006	25.7481
2007	19.05649
2008	14.48354
2009	19.56682
2010	18.72749
2011	14.41396
2012	16.8053
2013	20.3567
2014	30.70513
2015	31.99102
2016	39.56047