Year	%
1981	51.4
1986	39.6
1989	49.9
1990	49.6
1991	50.9
1992	50.3
1993	50.6
1994	51.5
1995	50.4
1996	51.2
1997	50.6
1998	50.8
1999	52.6
2000	52.1
2001	56.2
2002	56.7
2003	54
2004	53.4
2005	52.8
2006	54.7
2007	55
2008	54.1
2009	55.9
2010	53.6
2011	53.9
2012	53.6
2013	54.2
2014	53.9
2015	53.9
2016	54
2017	54
2018	53.3
2019	53.7
2020	54.4
2021	54.1
2022	52.7