Year	Percent
1988	15.92642
1989	15.98949
1990	16.68454
1991	18.68736
1992	18.44272
1993	19.14367
1994	18.6842
1995	19.18483
1996	18.89402
1997	21.1915
1998	22.26936
1999	22.82382
2000	24.60331
2001	23.48793
2002	21.47694
2003	19.72054
2004	19.75555
2005	20.26558
2006	21.46242
2007	18.47805
2008	19.97045
2009	22.64071
2010	24.91528
2011	23.71463
2012	25.36678
2013	25.89667
2014	26.09279
2015	26.84725
2016	26.66938