Year	per 1,000
1990	3.7
1991	3.5
1992	3.3
1993	3.1
1994	3
1995	2.8
1996	2.6
1997	2.5
1998	2.4
1999	2.3
2000	2.2
2001	2.1
2002	2
2003	1.9
2004	1.8
2005	1.7
2006	1.7
2007	1.6
2008	1.5
2009	1.4
2010	1.4
2011	1.3
2012	1.2
2013	1.2
2014	1.1
2015	1.1
2016	1
2017	1
2018	1
2019	0.9
2020	0.9
2021	0.9
2022	0.8