Year	%
1980	62.7
1988	57.3
1989	58
1991	55.8
1992	56.7
1996	60.8
1999	62.4
2000	62.2
2001	61.4
2002	60.6
2003	58.6
2004	60
2005	59
2008	59.7
2009	58.8
2010	59.2
2011	58.2
2012	57.3
2013	57.3
2014	57.2
2015	55.8
2016	55.5
2017	54.8
2018	55.4
2019	56.2
2020	57.9
2021	59.8
2022	59.6