Year	per 1,000
1990	4.2
1991	4.2
1992	4.3
1993	4.3
1994	4.3
1995	4.4
1996	4.3
1997	4.2
1998	4
1999	3.9
2000	3.7
2001	3.6
2002	3.4
2003	3.3
2004	3.2
2005	3.2
2006	3.1
2007	3.1
2008	3.1
2009	3.1
2010	3.1
2011	3.1
2012	3
2013	3
2014	3
2015	2.9
2016	2.9
2017	2.9
2018	2.9
2019	2.9
2020	2.9
2021	2.9
2022	2.9