Year	per 1,000
1990	2.4
1991	2.2
1992	2
1993	1.9
1994	1.8
1995	1.8
1996	1.7
1997	1.7
1998	1.6
1999	1.6
2000	1.6
2001	1.6
2002	1.6
2003	1.5
2004	1.4
2005	1.3
2006	1.2
2007	1.2
2008	1.1
2009	1.1
2010	1.1
2011	1
2012	1
2013	1
2014	1
2015	1
2016	1
2017	1
2018	1
2019	1
2020	1
2021	1.1
2022	1.1