Year	Percent
1988	15.9432
1989	17.77896
1990	18.03506
1991	19.34142
1992	19.76759
1993	20.24823
1994	22.65468
1995	26.02949
1996	24.06844
1997	26.63634
1998	27.07513
1999	32.14624
2000	35.06591
2001	29.78482
2002	31.52978
2003	32.31619
2004	32.91735
2005	32.47641
2006	32.14585
2007	30.54461
2008	27.59876
2009	28.73409
2010	29.46593
2011	25.72132
2012	26.17347
2013	27.09934
2014	26.88055
2015	26.84151
2016	26.58321