Year	per 1,000
1990	5
1991	5.1
1992	4.9
1993	4.7
1994	4.5
1995	4.3
1996	4.3
1997	4.2
1998	4.2
1999	4.1
2000	3.9
2001	3.7
2002	3.6
2003	3.5
2004	3.4
2005	3.4
2006	3.4
2007	3.4
2008	3.5
2009	3.4
2010	3.4
2011	3.3
2012	3.2
2013	3.1
2014	3
2015	2.9
2016	2.8
2017	2.8
2018	2.8
2019	2.9
2020	2.9
2021	3
2022	3.1