Year	%
2004	38
2005	35.8
2006	34.7
2007	34
2008	33.5
2009	33.4
2010	33.2
2011	33.2
2012	33
2013	33.1
2014	32.8
2015	31.8
2016	31.2
2017	29.7
2018	30.2
2019	28.8
2020	28.5
2021	28.5