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