Year	%
1997	38.4
1998	38.1
1999	37.4
2000	37.1
2001	36.9
2002	37.3
2003	40
2004	40.3
2005	41.3
2006	41
2007	42.3
2008	41.6
2009	39.8
2010	39.5
2011	39.7
2012	40.7
2013	40.9
2014	39.9
2015	37.7
2016	36.8
2017	37.2
2018	37.5
2019	37.7
2020	36