Year	%
1987	35.7
1992	34.5
1995	33.6
2000	34.2
2003	35.5
2004	34.9
2005	35.2
2006	35.8
2007	36.1
2008	35.2
2009	36.1
2010	36.7
2011	36.8
2012	37.3
2013	37.9
2014	37.7
2015	37.7
2016	37.6
2017	38.1
2018	37.7
2019	37.3
2020	37
2021	37.8