Year	%
1988	22.79
1989	31.6
1990	21.32
1991	27.4
1992	30.99
1993	27.16
1994	27.03
1995	18.55
1996	14.35
1997	14.66
1998	12.43
1999	16.84
2000	11.56
2001	10.86
2002	9.27
2003	9.63
2004	9.41
2005	8.48
2006	8.45
2007	8.53
2008	8.29
2009	7.93
2010	7.43
2011	7.92
2012	6.8
2013	7.55
2014	6.9
2015	7.34
2016	7.09
2017	7.36