Year	%
1977	25.9
1978	25.4
1979	25.2
1980	25.4
1981	24.5
1982	22.6
1983	22.8
1984	23.9
1986	23.6
1987	25
1989	24.7
1991	23.6
1993	25.7
1995	26.1
1998	27.6
2000	26.4
2002	25.8
2003	26.7
2004	26.3
2005	25.5
2006	25.6
2007	24.9
2008	25.7
2009	25.4
2010	26.2
2011	26.4
2012	26.4
2013	25.9
2014	25.5
2015	25.8
2016	26
2017	26.7
2018	25.9
2019	25.8
2020	26.1
2021	26.2