Year	%
1975	23.2
1981	23.5
1987	23.2
1992	23.2
1995	23.3
2000	22.5
2001	22.5
2002	22.8
2003	23.1
2004	22.9
2005	23.1
2006	22.9
2007	22.8
2008	22.8
2009	23
2010	22.8
2011	23
2012	23
2013	23.2
2014	22.9
2015	22.8
2016	22.8
2017	23.1
2018	23.2
2019	23
2020	23.1
2021	23.2