Year	%
1989	48.2
1990	45.5
1991	40.8
1992	41.4
1993	42.8
1994	43.5
1995	43.8
1996	43.7
1997	41.4
1998	44.6
1999	41.9
2001	41.6
2002	42.7
2003	45.1
2004	44.9
2005	46.1
2006	44
2007	43.1
2008	43
2009	38.4
2010	40.2
2011	39.7
2012	40.4
2013	37
2014	37.4
2015	36.6
2016	36
2017	36.6
2018	35.3
2019	34.6