Year	per 1,000
1990	7.4
1991	7.1
1992	6.8
1993	6.5
1994	6.2
1995	5.9
1996	5.6
1997	5.3
1998	5
1999	4.8
2000	4.5
2001	4.2
2002	4
2003	3.8
2004	3.6
2005	3.4
2006	3.2
2007	3.1
2008	3
2009	2.8
2010	2.7
2011	2.6
2012	2.6
2013	2.5
2014	2.4
2015	3.6
2016	2.2
2017	2.2
2018	2.1
2019	2
2020	2
2021	1.9
2022	1.9