Year	%
1979	23.8
1989	30.2
1991	28.7
1995	28.4
1997	26.8
1998	26.9
1999	26
2000	26.6
2001	27.7
2002	26.6
2003	25.7
2004	26
2005	25.2
2006	25.5
2007	25
2008	23.3
2009	23.2
2010	23.2
2011	22.9
2012	23
2013	23.9
2014	23.1
2015	22.6
2016	22.9
2017	23.5
2018	22.3
2019	22.8
2021	21.5
2023	22