Year	per 1,000
1990	7
1991	6.8
1992	6.5
1993	6.3
1994	6
1995	5.7
1996	5.4
1997	5.1
1998	4.9
1999	4.7
2000	4.4
2001	4.3
2002	4.1
2003	4
2004	3.9
2005	3.8
2006	3.7
2007	3.6
2008	3.5
2009	3.4
2010	3.4
2011	3.3
2012	3.2
2013	3.2
2014	3.1
2015	3.1
2016	3
2017	3
2018	2.9
2019	2.8
2020	2.8
2021	2.7
2022	2.7