Year	%
1977	22.8
1978	23
1979	23.2
1980	22.9
1981	22.7
1982	23.2
1983	23.3
1984	23.3
1986	23.4
1987	23.6
1989	23
1991	23.1
1993	23.4
1995	23.4
1998	22.7
2000	23
2002	23.1
2003	22.6
2004	22.6
2005	23
2006	22.8
2007	23
2008	22.8
2009	23.1
2010	22.8
2011	22.8
2012	22.8
2013	23.1
2014	23.3
2015	23.4
2016	23.2
2017	23
2018	23.2
2019	23.1
2020	23.1
2021	22.9