Year	%
1981	20.7
1988	20.3
1990	19.8
1992	19.5
1994	20.4
1996	20.4
1998	21.3
1999	20.6
2000	20.9
2002	20.9
2004	20.9
2006	21.4
2007	21.7
2008	21.7
2009	21.8
2010	21.7
2011	21.4
2012	21.8
2013	22.1
2014	22.1
2015	21.9
2016	21.8
2017	22.1
2018	22.2
2019	22.3
2020	22.4
2021	22.5