Year	per 1,000
1990	3.8
1991	3.6
1992	3.4
1993	3.2
1994	3
1995	2.9
1996	2.8
1997	2.7
1998	2.6
1999	2.6
2000	2.5
2001	2.4
2002	2.4
2003	2.3
2004	2.2
2005	2.1
2006	2
2007	2
2008	1.9
2009	1.8
2010	1.7
2011	1.6
2012	1.5
2013	1.5
2014	1.4
2015	1.4
2016	1.5
2017	1.3
2018	1.2
2019	1.2
2020	1.2
2021	1.2
2022	1.2