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