Year	per 1,000
1990	2.6
1991	2.5
1992	2.4
1993	2.3
1994	2.2
1995	2.1
1996	2
1997	1.9
1998	1.8
1999	1.7
2000	1.7
2001	1.6
2002	1.5
2003	1.5
2004	1.4
2005	1.4
2006	1.3
2007	1.3
2008	1.2
2009	1.1
2010	1.1
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