Year	per 1,000
1990	5.3
1991	5.2
1992	5
1993	4.8
1994	4.6
1995	4.3
1996	4.1
1997	3.8
1998	3.6
1999	3.4
2000	3.2
2001	3.1
2002	2.9
2003	2.8
2004	2.7
2005	2.5
2006	2.4
2007	2.3
2008	2.1
2009	2
2010	1.8
2011	1.7
2012	1.6
2013	1.6
2014	1.5
2015	1.5
2016	1.5
2017	1.5
2018	1.5
2019	1.5
2020	1.5
2021	1.5
2022	1.5