Year	per 1,000
1990	2.3
1991	1.8
1992	1.8
1993	1.7
1994	1.6
1995	1.5
1996	1.5
1997	1.4
1998	1.4
1999	1.3
2000	1.3
2001	1.3
2002	1.3
2003	1.3
2004	1.3
2005	1.3
2006	1.3
2007	1.3
2008	1.2
2009	1.2
2010	1.2
2011	1.1
2012	1.1
2013	1
2014	1
2015	1
2016	1
2017	1
2018	1
2019	1
2020	1
2021	1
2022	0.9