Year	%
2000	40.2
2001	39.6
2002	39.1
2003	38.8
2004	38.3
2005	37.8
2006	37.1
2007	36.3
2008	35.6
2009	34.9
2010	34.2
2011	33.5
2012	32.9
2013	32.4
2014	31.9
2015	31.6
2016	31.3
2017	31.1
2018	30.9
2019	30.9