Year	%
1975	24.3
1981	22.9
1987	23.1
1992	24.9
1995	25.2
2000	27
2001	26.5
2002	26.2
2003	25.3
2004	26.1
2005	26.8
2006	26.4
2007	27.1
2008	28.1
2009	27.3
2010	27.7
2011	27.6
2012	27.6
2013	28.8
2014	28.4
2015	29.2
2016	29.6
2017	28.8
2018	30
2019	29.3
2020	28.9
2021	29.8