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