Year	per 1,000
1990	6
1991	5.7
1992	5.4
1993	5.1
1994	4.8
1995	4.5
1996	4.3
1997	4.1
1998	3.8
1999	3.6
2000	3.4
2001	3.2
2002	3
2003	2.9
2004	2.7
2005	2.6
2006	2.5
2007	2.4
2008	2.3
2009	2.2
2010	2.1
2011	2
2012	1.9
2013	1.8
2014	1.7
2015	1.6
2016	1.5
2017	1.4
2018	1.4
2019	1.3
2020	1.3
2021	1.2
2022	1.2