Year	%
1975	34.2
1981	32.8
1987	33.2
1992	34.5
1995	34.4
2000	36.5
2001	36.3
2002	35.8
2003	34.7
2004	35.5
2005	35.6
2006	35.6
2007	36.2
2008	36.9
2009	36.2
2010	36.6
2011	36.3
2012	36.4
2013	37.1
2014	37
2015	37.6
2016	37.8
2017	37.1
2018	37.8
2019	37.5
2020	37.2
2021	37.7