Year	per 1,000
1990	3.6
1991	3.4
1992	3.3
1993	3.3
1994	3.3
1995	3.3
1996	3.3
1997	3.4
1998	3.3
1999	3.1
2000	2.9
2001	2.8
2002	2.7
2003	2.8
2004	2.9
2005	3.1
2006	3.3
2007	3.4
2008	3.4
2009	3.2
2010	2.8
2011	2.5
2012	2.3
2013	2.2
2014	2.2
2015	2.2
2016	2.2
2017	2.1
2018	2.1
2019	2.1
2020	2
2021	1.9
2022	1.8