Year	per 1,000
1990	2.9
1991	2.9
1992	2.8
1993	2.7
1994	2.5
1995	2.4
1996	2.3
1997	2.2
1998	2.1
1999	2
2000	1.9
2001	1.8
2002	1.7
2003	1.7
2004	1.6
2005	1.6
2006	1.5
2007	1.4
2008	1.4
2009	1.3
2010	1.2
2011	1.1
2012	1.1
2013	1
2014	0.9
2015	0.9
2016	0.8
2017	0.7
2018	0.7
2019	0.6
2020	0.6
2021	0.6
2022	0.5