Year	per 1,000
1990	2.3
1991	2.3
1992	2.2
1993	2.1
1994	2
1995	1.9
1996	1.8
1997	1.7
1998	1.7
1999	1.6
2000	1.5
2001	1.5
2002	1.4
2003	1.4
2004	1.3
2005	1.3
2006	1.2
2007	1.2
2008	1.2
2009	1.1
2010	1.1
2011	1
2012	1
2013	0.9
2014	0.9
2015	0.8
2016	0.8
2017	0.7
2018	0.7
2019	0.6
2020	0.6
2021	0.6
2022	0.5