Year	per 1,000
1990	2.6
1991	2.5
1992	2.3
1993	2.2
1994	2.2
1995	2.1
1996	2
1997	2
1998	1.9
1999	1.9
2000	1.8
2001	1.7
2002	1.7
2003	1.7
2004	1.6
2005	1.6
2006	1.6
2007	1.5
2008	1.5
2009	1.5
2010	1.5
2011	1.5
2012	1.5
2013	1.5
2014	1.5
2015	1.5
2016	1.5
2017	1.4
2018	1.3
2019	1.2
2020	1.1
2021	1
2022	0.9