Year	per 1,000
1990	5.3
1991	5.2
1992	5.1
1993	5
1994	4.9
1995	4.8
1996	4.8
1997	4.7
1998	4.7
1999	4.6
2000	4.6
2001	4.5
2002	4.5
2003	4.4
2004	4.3
2005	4.3
2006	4.2
2007	4.1
2008	4
2009	3.9
2010	3.8
2011	3.7
2012	3.6
2013	3.6
2014	3.5
2015	3.5
2016	3.4
2017	3.4
2018	3.4
2019	3.3
2020	3.3
2021	3.2
2022	3.2