Year	per 1,000
1990	3
1991	3
1992	3
1993	2.9
1994	2.8
1995	2.8
1996	2.7
1997	2.6
1998	2.6
1999	2.6
2000	2.5
2001	2.4
2002	2.3
2003	2.1
2004	2
2005	1.9
2006	1.8
2007	1.8
2008	1.7
2009	1.6
2010	1.6
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	1.1
2021	1
2022	1