Year	Percent
1987	35.9
1989	31
1992	29.8
1995	30.3
1998	25.8
1999	22.8
2000	24.8
2001	23.4
2002	23
2003	23.1
2004	19.7
2005	24.4
2007	19.6
2010	18.6
2013	19.9