Year	per 1,000
1990	6.7
1991	6.6
1992	6.5
1993	6.4
1994	6.3
1995	6.2
1996	6.1
1997	6
1998	5.9
1999	5.8
2000	5.8
2001	5.7
2002	5.7
2003	5.6
2004	5.5
2005	5.4
2006	5.3
2007	5.1
2008	4.9
2009	4.7
2010	4.5
2011	4.4
2012	4.3
2013	4.2
2014	4.1
2015	4
2016	4
2017	4
2018	4
2019	4
2020	4
2021	3.9
2022	3.8