Year	per 1,000
1990	6.5
1991	6.3
1992	6.1
1993	5.9
1994	5.7
1995	5.6
1996	5.4
1997	5.2
1998	5.1
1999	5
2000	4.8
2001	4.7
2002	4.6
2003	4.5
2004	4.3
2005	4.2
2006	4.1
2007	4
2008	3.9
2009	3.8
2010	3.7
2011	3.6
2012	3.5
2013	3.4
2014	3.3
2015	3.2
2016	3.2
2017	3.1
2018	3
2019	2.9
2020	2.8
2021	2.7
2022	2.7