Year	per 1,000
1990	3.5
1991	3.5
1992	3.6
1993	3.6
1994	3.6
1995	3.5
1996	3.4
1997	3.3
1998	3.2
1999	3
2000	2.9
2001	2.8
2002	2.7
2003	2.6
2004	2.6
2005	2.6
2006	2.6
2007	2.6
2008	2.6
2009	2.6
2010	2.5
2011	2.4
2012	2.4
2013	2.3
2014	2.3
2015	2.2
2016	2.2
2017	2.2
2018	2.2
2019	2.2
2020	2.3
2021	2.3
2022	2.3