Year	per 1,000
1990	2
1991	2
1992	2
1993	2
1994	2
1995	2
1996	1.9
1997	1.9
1998	1.9
1999	1.8
2000	1.8
2001	1.7
2002	1.7
2003	1.6
2004	1.5
2005	1.5
2006	1.4
2007	1.3
2008	1.3
2009	1.2
2010	1.2
2011	1.2
2012	1.1
2013	1.1
2014	1
2015	1
2016	1
2017	1
2018	0.9
2019	0.9
2020	0.9
2021	0.8
2022	0.8