Year	per 1,000
1990	3.6
1991	3.3
1992	3.1
1993	3
1994	2.8
1995	2.6
1996	2.5
1997	2.3
1998	2.2
1999	2.1
2000	2
2001	1.9
2002	1.8
2003	1.7
2004	1.6
2005	1.5
2006	1.4
2007	1.4
2008	1.3
2009	1.3
2010	1.2
2011	1.2
2012	1.1
2013	1.1
2014	1.1
2015	1
2016	1
2017	1
2018	0.9
2019	0.9
2020	0.9
2021	0.8
2022	0.8