Year	per 1,000
1990	3.1
1991	2.9
1992	2.7
1993	2.6
1994	2.4
1995	2.3
1996	2.2
1997	2.2
1998	2.4
1999	2
2000	2
2001	2.7
2002	1.9
2003	1.9
2004	1.9
2005	1.9
2006	1.9
2007	1.9
2008	1.9
2009	2
2010	1.9
2011	1.9
2012	1.9
2013	1.9
2014	2
2015	2
2016	2.1
2017	2.2
2018	2.3
2019	2.3
2020	2.4
2021	2.4
2022	2.4