Year	%
1988	2.24
1989	4.31
1990	10.81
1991	9.66
1992	9.61
1993	6.59
1994	9.21
1995	9.97
1996	6.69
1997	5.97
1998	4.07
1999	3.82
2000	3.21
2001	4.27
2002	4.43
2003	2.79
2004	2.64
2005	4.21
2006	2.41
2007	3.8
2008	4.03
2009	3.64
2010	3.08
2011	3.72
2012	3.71
2013	3.78
2014	3.62
2015	2.52
2016	2.45
2017	2.74