Year	per 1,000
1990	5.2
1991	5
1992	4.8
1993	4.7
1994	4.5
1995	4.4
1996	4.2
1997	4.1
1998	3.9
1999	3.8
2000	3.7
2001	3.6
2002	3.4
2003	3.3
2004	3.2
2005	3.1
2006	3
2007	2.9
2008	2.8
2009	2.7
2010	2.6
2011	2.6
2012	2.5
2013	2.4
2014	2.3
2015	2.2
2016	2.2
2017	2.1
2018	2
2019	2
2020	1.9
2021	1.9
2022	1.8