Year	per 1,000
1990	5.4
1991	5.2
1992	5
1993	4.8
1994	4.6
1995	4.5
1996	4.3
1997	4.1
1998	3.9
1999	3.8
2000	3.6
2001	3.4
2002	3.2
2003	3.4
2004	2.9
2005	2.8
2006	2.7
2007	2.6
2008	2.5
2009	2.4
2010	2.3
2011	2.2
2012	2.2
2013	2.1
2014	2.1
2015	2
2016	1.9
2017	1.8
2018	1.7
2019	1.6
2020	1.5
2021	1.4
2022	1.3