Year	per 1,000
1990	4.1
1991	3.9
1992	3.8
1993	3.6
1994	3.5
1995	3.3
1996	3.2
1997	3
1998	2.9
1999	2.7
2000	2.6
2001	2.5
2002	2.3
2003	2.2
2004	2.1
2005	2
2006	1.9
2007	1.8
2008	1.7
2009	1.6
2010	1.5
2011	1.5
2012	1.4
2013	1.4
2014	1.3
2015	1.3
2016	1.2
2017	1.2
2018	1.1
2019	1.1
2020	1
2021	1
2022	1