Year	per 1,000
1990	5.4
1991	5.1
1992	4.7
1993	4.3
1994	4
1995	3.8
1996	3.5
1997	3.3
1998	3.1
1999	2.9
2000	2.7
2001	2.6
2002	2.4
2003	2.3
2004	4.1
2005	2.1
2006	2
2007	1.8
2008	1.7
2009	1.6
2010	1.5
2011	1.4
2012	1.3
2013	1.2
2014	1.1
2015	1
2016	0.9
2017	0.9
2018	0.8
2019	0.7
2020	0.6
2021	0.6
2022	0.5