Year	%
1983	37.5
1987	36.6
1990	39.7
1993	38.6
1999	37.1
2004	38.3
2005	38
2006	39
2007	38.6
2008	38.1
2009	37
2010	36.9
2011	37
2012	37
2013	37.2
2014	37.7
2015	37.4
2016	37.2
2017	37.6
2018	37.2
2019	38
2020	35.4
2021	35.3