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