Year	%
1988	24.74
1989	34.52
1990	22.78
1991	31.36
1992	30.94
1993	28.44
1994	23.92
1995	25.14
1996	13.47
1997	14.74
1998	11.66
1999	15.07
2000	10.03
2001	10.77
2002	10.3
2003	10.38
2004	9.87
2005	9.16
2006	9.58
2007	9.8
2008	9.44
2009	9.44
2010	8.35
2011	8.35
2012	7.99
2013	8.16
2014	8.95
2015	8.42
2016	8.37
2017	9.14