Year	per 1,000
1990	2.5
1991	2.4
1992	2.4
1993	2.3
1994	2.2
1995	2.1
1996	2
1997	1.9
1998	1.8
1999	1.7
2000	1.6
2001	1.5
2002	1.4
2003	1.3
2004	1.2
2005	1.1
2006	1.1
2007	1
2008	1
2009	0.9
2010	0.8
2011	0.8
2012	0.8
2013	0.7
2014	0.7
2015	0.6
2016	0.6
2017	0.6
2018	0.5
2019	0.5
2020	0.5
2021	0.5
2022	0.4