Year	per 1,000
1990	4.8
1991	4.8
1992	4.6
1993	4.6
1994	4.8
1995	4.4
1996	4.3
1997	4.2
1998	4.1
1999	4
2000	3.9
2001	3.8
2002	3.7
2003	3.7
2004	3.7
2005	3.6
2006	3.6
2007	3.5
2008	3.6
2009	3.4
2010	3.4
2011	3.3
2012	3.2
2013	3.1
2014	3.1
2015	3
2016	2.9
2017	2.9
2018	2.8
2019	2.7
2020	2.7
2021	2.6
2022	2.6