Year	per 1,000
1990	4.9
1991	5.1
1992	5.2
1993	5.3
1994	5.2
1995	5
1996	4.8
1997	4.6
1998	4.5
1999	4.4
2000	4.4
2001	4.4
2002	4.4
2003	4.3
2004	4.3
2005	4.2
2006	4.2
2007	4.1
2008	3.9
2009	3.7
2010	3.5
2011	3.4
2012	3.2
2013	3
2014	2.9
2015	2.7
2016	2.5
2017	2.4
2018	2.3
2019	2.2
2020	2.1
2021	2
2022	1.9