Year	per 1,000
1990	6.9
1991	6.3
1992	5.7
1993	5.2
1994	4.8
1995	4.5
1996	4.2
1997	4
1998	3.7
1999	3.5
2000	3.3
2001	3.1
2002	2.9
2003	2.8
2004	3.8
2005	2.6
2006	2.6
2007	2.5
2008	2.5
2009	2.5
2010	2.5
2011	2.5
2012	2.4
2013	2.3
2014	2.2
2015	2.1
2016	2
2017	1.8
2018	1.7
2019	1.6
2020	1.5
2021	1.4
2022	1.3