Year	per 1,000
1990	2.1
1991	2.1
1992	2
1993	2
1994	1.9
1995	1.8
1996	1.7
1997	1.7
1998	1.6
1999	1.6
2000	1.5
2001	1.5
2002	1.4
2003	1.4
2004	1.3
2005	1.2
2006	1.2
2007	1.2
2008	1.1
2009	1.1
2010	1
2011	1
2012	0.9
2013	0.9
2014	0.8
2015	0.8
2016	0.7
2017	0.7
2018	0.6
2019	0.6
2020	0.5
2021	0.5
2022	0.5