Year	per 1,000
1990	7.1
1991	6.8
1992	6.5
1993	6.2
1994	5.9
1995	5.6
1996	5.4
1997	5.1
1998	4.9
1999	4.7
2000	4.5
2001	4.4
2002	4.2
2003	4.1
2004	3.9
2005	3.9
2006	3.8
2007	3.7
2008	3.6
2009	3.5
2010	3.4
2011	3.3
2012	3.2
2013	3
2014	2.9
2015	2.8
2016	2.6
2017	2.5
2018	2.3
2019	2.2
2020	2
2021	1.9
2022	1.8