Year	per 1,000
1990	5.2
1991	4.9
1992	4.6
1993	4.3
1994	4.1
1995	3.9
1996	3.6
1997	3.4
1998	3.2
1999	3.1
2000	2.9
2001	2.7
2002	2.6
2003	2.5
2004	2.4
2005	2.3
2006	2.2
2007	2.1
2008	2
2009	1.9
2010	1.8
2011	1.8
2012	1.7
2013	1.6
2014	1.6
2015	1.5
2016	1.5
2017	1.4
2018	1.4
2019	1.3
2020	1.3
2021	1.3
2022	1.2