Year	per 1,000
1990	6.7
1991	6.8
1992	6.4
1993	6.2
1994	6.1
1995	6
1996	5.9
1997	5.7
1998	5.6
1999	5.4
2000	5.2
2001	5.1
2002	5
2003	4.9
2004	4.8
2005	4.8
2006	4.6
2007	4.5
2008	4.6
2009	4.3
2010	4.3
2011	4.1
2012	3.9
2013	3.8
2014	3.7
2015	3.6
2016	3.5
2017	3.4
2018	3.3
2019	3.2
2020	3.1
2021	3
2022	2.9