Year	%
1988	22.67
1989	23.05
1990	26.58
1992	20.65
1993	17.15
1994	21.64
1995	18
1996	12.45
1997	13.61
1998	13.79
1999	17.31
2000	14.74
2001	14.73
2002	12.53
2003	13.84
2004	12.49
2005	10.86
2006	9.27
2007	9.16
2008	7.14
2009	7.52
2010	7.58
2011	7.32
2012	6.5
2013	6.57
2014	8.03
2015	7.71
2016	7.69
2017	6.77