Year	per 1,000
1990	8.4
1991	8.5
1992	8.5
1993	8.4
1994	8.4
1995	8.2
1996	8
1997	7.8
1998	7.5
1999	7.2
2000	6.9
2001	6.5
2002	6.2
2003	5.8
2004	5.4
2005	5.1
2006	4.8
2007	4.5
2008	4.2
2009	3.9
2010	3.6
2011	3.4
2012	3.2
2013	2.9
2014	2.7
2015	2.5
2016	2.3
2017	2.2
2018	2.1
2019	2
2020	1.9
2021	1.8
2022	1.7