Year	%
2000	19.5
2001	18.9
2002	18.4
2003	18
2004	17.7
2005	17.5
2006	17.4
2007	17.3
2008	17.3
2009	17.3
2010	17.3
2011	17.4
2012	17.5
2013	17.5
2014	17.6
2015	17.7
2016	17.9
2017	18
2018	18.1
2019	18.3