Year	per 1,000
1990	3.6
1991	3.6
1992	3.6
1993	3.5
1994	3.5
1995	3.3
1996	3.2
1997	3
1998	2.9
1999	2.8
2000	2.7
2001	2.7
2002	2.6
2003	2.6
2004	2.5
2005	2.5
2006	2.4
2007	2.3
2008	2.2
2009	2.1
2010	1.9
2011	1.8
2012	1.7
2013	1.6
2014	1.5
2015	1.4
2016	1.4
2017	1.4
2018	1.4
2019	1.4
2020	1.4
2021	1.4
2022	1.5