Year	per 1,000
1990	4.1
1991	3.9
1992	3.7
1993	3.6
1994	3.5
1995	3.4
1996	3.3
1997	3.3
1998	3.2
1999	3.2
2000	3.1
2001	3
2002	3
2003	3
2004	3
2005	3
2006	2.9
2007	2.9
2008	2.8
2009	2.7
2010	2.7
2011	2.6
2012	2.6
2013	2.6
2014	2.5
2015	2.6
2016	2.7
2017	2.8
2018	2.9
2019	2.9
2020	3
2021	3.2
2022	3.4