Year	%
1979	26.9
1986	26.9
1992	26.9
1997	28.2
2001	28.7
2002	28.7
2003	29.4
2004	29.3
2005	30.4
2006	29.7
2007	29.5
2008	30
2009	30.5
2010	31.1
2011	29.5
2012	29.5
2013	28.6
2014	28.2
2015	28.6
2016	27.7
2017	27
2018	27.6
2019	27.1
2020	26.7
2021	27.1