Year	%
2000	34.9
2001	34.6
2002	34.4
2003	34.2
2004	33.7
2005	34
2006	34.3
2007	33.9
2008	34
2009	33.4
2010	32.7
2011	30.8
2012	30.1
2013	27.1
2014	24.5
2015	23.8
2016	22.8
2017	22.5
2018	21.7
2019	21.5