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