Year	per 1,000
1990	3.4
1991	3.4
1992	3.4
1993	3.5
1994	3.5
1995	3.5
1996	3.6
1997	3.6
1998	3.6
1999	3.7
2000	3.7
2001	3.8
2002	3.8
2003	3.8
2004	3.8
2005	3.7
2006	3.5
2007	3.3
2008	3.1
2009	2.9
2010	2.7
2011	2.6
2012	2.4
2013	2.3
2014	2.1
2015	2
2016	1.9
2017	1.9
2018	1.8
2019	1.8
2020	1.9
2021	1.9
2022	1.9