Year	Percent
1987	5.67
1988	4.91
1989	4.54
1990	5.11
1991	4.37
1992	3.59
1993	3.56
1994	3.43
1995	3.74
1996	3.18
1997	3.09
1998	3.29
1999	2.97
2000	2.56
2001	2.9
2002	3.1
2003	2.64
2004	2.38
2005	2.29
2006	2.24
2007	1.82
2008	1.55
2009	1.61
2010	2.82
2011	1.81
2012	1.82
2013	2.38
2014	2.31
2015	2.54
2016	2.22
2017	1.98