Year	per 1,000
1990	6.9
1991	7.3
1992	6.6
1993	6.5
1994	6.4
1995	6.2
1996	6.1
1997	5.9
1998	5.7
1999	5.5
2000	5.3
2001	5.1
2002	5
2003	4.9
2004	4.8
2005	4.9
2006	4.5
2007	4.4
2008	4.3
2009	4.1
2010	4
2011	3.8
2012	3.6
2013	3.5
2014	3.3
2015	3.2
2016	3.1
2017	3
2018	2.9
2019	2.7
2020	2.6
2021	2.5
2022	2.5