Year	%
1996	37.1
1997	40.7
1998	41.3
1999	40.1
2000	40.5
2001	39.6
2002	37.2
2003	36.7
2004	36.2
2005	37.4
2006	36.9
2007	38.1
2008	38.5
2009	38.2
2010	39.5
2011	39.6
2012	39
2013	38.6
2014	37.6
2015	36.5
2016	36.6
2017	37.9
2018	36.4
2019	35.9
2020	34.5
2021	34.2