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