Year	per 1,000
1990	5
1991	4.8
1992	4.6
1993	4.5
1994	4.4
1995	4.3
1996	4.2
1997	4
1998	3.9
1999	3.7
2000	3.6
2001	3.5
2002	3.4
2003	3.3
2004	3.3
2005	3.2
2006	3.2
2007	3.1
2008	3
2009	2.9
2010	2.8
2011	2.7
2012	2.6
2013	2.4
2014	2.3
2015	2.2
2016	2.2
2017	2.1
2018	2.1
2019	2
2020	2
2021	2
2022	1.9