Year	%
1977	41.4
1978	40.5
1979	40.3
1980	40.4
1981	39.6
1982	37.6
1983	37.8
1984	39.1
1986	38.8
1987	40.8
1989	39.8
1991	38.8
1993	41.2
1995	41.4
1998	42.7
2000	41.7
2002	41.2
2003	41.8
2004	41.3
2005	40.7
2006	40.8
2007	40.1
2008	40.8
2009	40.7
2010	41.4
2011	41.7
2012	41.7
2013	41.4
2014	41
2015	41.4
2016	41.4
2017	42.1
2018	41.5
2019	41.1
2020	41.7
2021	41.6