Year	per 1,000
1990	4.6
1991	4.6
1992	4.5
1993	4.4
1994	4.3
1995	4.1
1996	3.9
1997	3.7
1998	3.4
1999	3.2
2000	2.9
2001	2.8
2002	2.6
2003	2.4
2004	2.3
2005	2.2
2006	2.2
2007	2.1
2008	2
2009	2
2010	2
2011	2
2012	2
2013	1.9
2014	1.9
2015	1.9
2016	1.9
2017	1.9
2018	2
2019	2
2020	2.1
2021	2.2
2022	2.3