Year	per 1,000
1990	5.3
1991	5.2
1992	5.2
1993	5.1
1994	4.9
1995	4.8
1996	4.6
1997	4.5
1998	4.3
1999	4.1
2000	4
2001	3.8
2002	3.6
2003	3.4
2004	3.3
2005	3.1
2006	3
2007	2.9
2008	2.8
2009	2.7
2010	2.6
2011	2.6
2012	2.6
2013	2.5
2014	2.5
2015	2.6
2016	2.8
2017	2.6
2018	2.7
2019	2.7
2020	2.8
2021	2.8
2022	2.8