Year	per 1,000
1990	3.9
1991	3.9
1992	3.8
1993	3.7
1994	3.6
1995	3.5
1996	3.4
1997	3.3
1998	3.2
1999	3.1
2000	3
2001	2.9
2002	2.8
2003	2.7
2004	2.6
2005	2.5
2006	2.5
2007	2.4
2008	2.3
2009	2.3
2010	2.3
2011	2.3
2012	2.3
2013	2.3
2014	2.4
2015	2.4
2016	2.5
2017	2.6
2018	2.6
2019	2.7
2020	2.6
2021	2.6
2022	2.6