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