Year	per 1,000
1990	5.9
1991	5.3
1992	4.9
1993	4.5
1994	4.2
1995	4
1996	3.8
1997	3.6
1998	3.4
1999	3.2
2000	3.1
2001	2.9
2002	2.8
2003	2.7
2004	2.6
2005	2.6
2006	2.6
2007	2.7
2008	2.7
2009	2.8
2010	2.8
2011	2.7
2012	2.7
2013	2.6
2014	2.5
2015	2.5
2016	2.4
2017	2.3
2018	2.2
2019	2.1
2020	2
2021	1.9
2022	1.8