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