Year	per 1,000
1990	3.4
1991	3.5
1992	4.1
1993	3.7
1994	3.7
1995	3.7
1996	3.6
1997	3.4
1998	3.3
1999	3.1
2000	3
2001	2.9
2002	2.8
2003	2.7
2004	2.5
2005	2.4
2006	2.2
2007	2.1
2008	2
2009	1.9
2010	1.8
2011	1.7
2012	1.7
2013	1.7
2014	1.6
2015	1.6
2016	1.6
2017	1.6
2018	1.6
2019	1.6
2020	1.8
2021	1.5
2022	1.5