Year	per 1,000
1990	5.5
1991	5.4
1992	5.4
1993	5.2
1994	5
1995	4.8
1996	4.5
1997	4.2
1998	3.9
1999	3.6
2000	3.4
2001	3.2
2002	3
2003	2.8
2004	2.7
2005	2.5
2006	2.4
2007	2.2
2008	2.1
2009	2
2010	1.8
2011	1.7
2012	1.6
2013	1.5
2014	1.4
2015	1.3
2016	1.2
2017	1.2
2018	1.1
2019	1.1
2020	1
2021	1
2022	1