Year	%
1979	53.4
1989	61
1991	60.6
1995	60.5
1997	61.3
1998	60.6
1999	59.8
2000	60.1
2001	59.9
2002	59.8
2003	59.5
2004	58.7
2005	57.7
2006	58.4
2007	56.6
2008	57
2009	56.4
2010	56
2011	55.8
2012	56.1
2013	56
2014	54.8
2015	55.3
2016	54.8
2017	54.2
2018	53.6
2019	54.4
2021	55.7
2023	53.5