Year	per 1,000
1990	5
1991	4.8
1992	4.5
1993	4.3
1994	4
1995	3.8
1996	3.5
1997	3.3
1998	3.1
1999	2.9
2000	2.7
2001	2.6
2002	2.4
2003	2.3
2004	2.2
2005	2.1
2006	2
2007	1.9
2008	1.8
2009	1.8
2010	1.7
2011	2.9
2012	1.6
2013	1.6
2014	1.5
2015	1.5
2016	1.4
2017	1.4
2018	1.3
2019	1.3
2020	1.2
2021	1.2
2022	1.2