Year	per 1,000
1990	2.5
1991	2.5
1992	2.4
1993	2.3
1994	2.3
1995	2.2
1996	2.1
1997	2.1
1998	2
1999	2
2000	1.9
2001	1.9
2002	1.9
2003	1.8
2004	1.8
2005	1.8
2006	1.7
2007	1.7
2008	1.7
2009	1.7
2010	1.6
2011	1.6
2012	1.6
2013	1.6
2014	1.5
2015	1.5
2016	1.5
2017	1.4
2018	1.4
2019	1.4
2020	1.3
2021	1.3
2022	1.3