Year	per 1,000
1990	4.8
1991	4.7
1992	4.5
1993	4.3
1994	4.2
1995	4
1996	3.8
1997	3.7
1998	8.5
1999	3.3
2000	3.2
2001	3
2002	2.8
2003	2.7
2004	2.5
2005	2.4
2006	2.3
2007	2.2
2008	2.1
2009	2
2010	1.9
2011	1.8
2012	1.8
2013	1.7
2014	1.6
2015	1.6
2016	1.5
2017	1.4
2018	1.4
2019	1.3
2020	1.3
2021	1.3
2022	1.2