Year	per 1,000
1990	6.3
1991	6.4
1992	6.3
1993	6.2
1994	6.1
1995	6
1996	5.9
1997	5.7
1998	5.4
1999	5.1
2000	4.7
2001	4.4
2002	4
2003	3.7
2004	3.4
2005	3.2
2006	3
2007	2.8
2008	2.7
2009	2.5
2010	2.3
2011	2.2
2012	2
2013	1.9
2014	1.8
2015	1.7
2016	1.7
2017	1.7
2018	1.7
2019	1.7
2020	1.7
2021	1.8
2022	1.9