Year	Percent
1987	3.9
1990	6.7
1991	5.4
1992	4.5
1993	4
1994	3.9
1995	4.1
1996	4.4
1997	4.5
1998	4.6
1999	4.1
2000	3.9
2001	4
2002	4.2
2003	4.6
2004	4.5
2005	4.1
2006	3.9
2007	3.7
2008	3.2
2009	2.9