Year	per 1,000
1990	3.1
1991	3
1992	2.8
1993	2.7
1994	2.6
1995	2.5
1996	2.4
1997	2.3
1998	2.6
1999	2.2
2000	2.1
2001	2.1
2002	2
2003	2
2004	2
2005	1.9
2006	1.8
2007	1.8
2008	1.7
2009	1.7
2010	2.5
2011	1.6
2012	1.5
2013	1.5
2014	1.4
2015	1.4
2016	1.4
2017	1.3
2018	1.3
2019	1.3
2020	1.2
2021	1.2
2022	1.2