Year	per 1,000
1990	6.9
1991	6.6
1992	6.4
1993	6.2
1994	6
1995	5.9
1996	5.6
1997	5.4
1998	5.2
1999	5
2000	4.8
2001	4.6
2002	4.5
2003	4.3
2004	4.2
2005	4
2006	3.9
2007	3.8
2008	3.7
2009	3.6
2010	3.5
2011	3.4
2012	3.4
2013	3.3
2014	3.3
2015	3.2
2016	3.2
2017	3.2
2018	3.1
2019	3.1
2020	3.1
2021	3
2022	3