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