Year	%
1975	19.4
1981	18.3
1987	19
1992	20.1
1995	20
2000	22.2
2001	21.9
2002	21.3
2003	20.1
2004	21.1
2005	21.1
2006	21.1
2007	21.7
2008	22.4
2009	21.5
2010	21.8
2011	21.6
2012	21.6
2013	22.2
2014	22.2
2015	22.9
2016	23.3
2017	22.3
2018	22.9
2019	22.7
2020	22.4
2021	22.7