Year	per 1,000
1990	2.7
1991	2.8
1992	2.7
1993	2.6
1994	2.5
1995	2.4
1996	2.3
1997	2.3
1998	2.2
1999	2.2
2000	2.1
2001	2.1
2002	2
2003	1.9
2004	1.9
2005	1.8
2006	1.7
2007	1.7
2008	1.6
2009	1.5
2010	1.4
2011	1.3
2012	1.3
2013	1.2
2014	1.1
2015	1.1
2016	1.1
2017	1
2018	1
2019	1
2020	1
2021	1
2022	1