Year	%
1970	22.2
1975	22.2
1979	22.4
1984	22.4
1990	22.5
1996	22.9
1997	22.8
1998	22.8
1999	22.5
2000	22.5
2001	22.4
2002	22.5
2003	22.3
2004	22.4
2005	22.5
2006	22.7
2007	21.9
2008	21.9
2009	22.1
2010	21.8
2011	21.8
2012	21.8
2013	21.8
2014	22
2015	21.7
2016	22
2017	21.9
2018	21.6
2019	22.4
2020	22.5
2021	22.5