Year	%
1979	36.3
1986	36.5
1992	35.5
1997	38.1
2001	38.9
2002	39.6
2003	40.7
2004	41.5
2005	42.3
2006	41.6
2007	41.1
2008	41.6
2009	42.6
2010	42.6
2011	41.4
2012	41.3
2013	39.9
2014	39.8
2015	39.7
2016	39
2017	38.2
2018	38.6
2019	38.3
2020	37.8
2021	37.9