Year	%
2000	31.8
2001	31.4
2002	31.1
2003	31
2004	30.9
2005	30.7
2006	30.5
2007	30.2
2008	29.9
2009	29.7
2010	29.5
2011	29.4
2012	29.3
2013	29.2
2014	29.1
2015	29.1
2016	29
2017	29
2018	28.9
2019	29