Year	Percent
1990	18.6681
1991	17.68152
1992	15.48512
1993	15.9932
1994	15.46558
1995	20.75788
1996	20.08817
1997	20.97339
1998	22.26286
1999	19.69809
2000	21.8801
2001	17.35508
2002	20.83022
2003	17.92932
2004	21.04556
2005	19.84522
2006	21.40814
2007	23.71242
2008	27.93271
2009	25.74248
2010	24.46832
2011	26.91292
2012	28.92696
2013	28.80785
2014	30.29523
2015	30.44246
2016	32.58978
2017	31.63356