Year	%
1970	28.6
1975	27.9
1979	26.6
1984	26.1
1990	25.2
1996	24.5
1997	24.5
1998	24.5
1999	25.3
2000	25.4
2001	25.4
2002	25
2003	25.2
2004	24.5
2005	23.9
2006	23.5
2007	26.2
2008	26.7
2009	26.1
2010	27.1
2011	26.9
2012	26.9
2013	26.4
2014	26.1
2015	26.6
2016	25.9
2017	25.8
2018	26.7
2019	24.8
2020	24.5
2021	24.9