Year	Percent
1990	17.71
1991	18.19
1992	24.09
1993	33.7
1994	34.49
1995	32.2
1996	30.58
1997	29.6
1998	28.63
1999	30.03
2000	31.04
2001	30.68
2002	29.95
2003	29.57
2004	28.92
2005	28.1
2006	27.75
2007	23.48
2008	25.04
2009	29.48
2010	29.21