Year	per 1,000
1990	5.5
1991	5.4
1992	5.4
1993	5.3
1994	5.3
1995	5.2
1996	5
1997	4.9
1998	4.7
1999	4.7
2000	4.5
2001	4.4
2002	4.3
2003	4.2
2004	4.2
2005	3.9
2006	3.7
2007	3.7
2008	3.6
2009	3.5
2010	3.5
2011	3.5
2012	3.5
2013	3.4
2014	3.4
2015	3.3
2016	3.3
2017	3.2
2018	3.1
2019	3.1
2020	3
2021	2.9
2022	2.9