Year	per 1,000
1990	6.7
1991	6.5
1992	6.3
1993	6.1
1994	5.9
1995	5.7
1996	5.5
1997	5.4
1998	5.2
1999	5
2000	4.9
2001	4.7
2002	4.6
2003	4.5
2004	4.3
2005	4.2
2006	4.7
2007	4
2008	3.9
2009	3.8
2010	3.7
2011	3.6
2012	3.5
2013	3.5
2014	3.4
2015	3.3
2016	3.3
2017	3.2
2018	3.1
2019	3.1
2020	3
2021	2.9
2022	2.9