Year	%
1990	32.1
1991	31.4
1992	30.8
1993	30.2
1994	29.7
1995	29.2
1996	28.8
1997	28.4
1998	28
1999	27.6
2000	27.2
2001	26.9
2002	26.7
2003	26.5
2004	26.3
2005	26.1
2006	25.9
2007	25.6
2008	25.4
2009	25.3
2010	25.2
2011	25.2
2012	25.3
2013	25.4
2014	25.5
2015	25.8
2016	26.2