Year	Percent
1990	28.20513
1991	24.38198
1992	27.12209
1993	20.79433
1994	17.58105
1995	24.80431
1996	26.32783
1997	29.53903
1998	30.14226
1999	33.26885
2000	30.6783
2001	30.42186
2002	30.57245
2003	30.0812
2004	30.08303
2005	29.73164
2006	30.87491
2007	30.81161
2008	32.19036
2009	38.87739
2010	37.03316
2011	36.06899
2012	45.69893
2013	45.74976
2014	47.41304
2015	48.21267
2016	49.91051
2017	51.31796