Year	%
1999	15.4
2001	15.6
2002	15.6
2003	15.9
2004	15
2005	15.2
2006	17
2007	16.7
2008	17
2009	17.2
2010	16.8
2011	17
2012	17.1
2013	16.9
2014	16.9
2015	16.7
2016	17
2017	15.9