Year	%
1988	4.79
1989	6.23
1990	6.82
1991	6.14
1992	7.17
1993	7.42
1994	8.57
1995	6.44
1996	6.15
1997	5.42
1998	5.22
1999	5.21
2000	4.96
2001	5.38
2002	4.56
2003	4.57
2004	3.72
2005	3.5
2006	3.16
2007	3.38
2008	3.31
2009	3.2
2010	3.3
2011	3.53
2012	2.89
2013	3.04
2014	2.87
2015	3.06
2016	2.98
2017	2.59