Year	per 1,000
1990	2.5
1991	2.4
1992	2.4
1993	2.4
1994	2.4
1995	2.5
1996	2.7
1997	2.8
1998	2.8
1999	2.8
2000	2.8
2001	2.7
2002	2.6
2003	2.5
2004	2.5
2005	2.4
2006	2.4
2007	2.3
2008	2.2
2009	2
2010	1.9
2011	1.7
2012	1.6
2013	1.4
2014	1.3
2015	1.2
2016	1.1
2017	1.1
2018	1
2019	0.9
2020	0.9
2021	0.9
2022	0.9