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