Year	per 1,000
1990	4.5
1991	4.3
1992	4.1
1993	3.9
1994	3.7
1995	3.5
1996	3.4
1997	3.2
1998	3.1
1999	3
2000	2.9
2001	2.8
2002	2.7
2003	2.6
2004	3
2005	2.4
2006	2.3
2007	2.2
2008	2.2
2009	2
2010	1.9
2011	1.9
2012	1.8
2013	1.7
2014	1.6
2015	1.6
2016	1.5
2017	1.5
2018	1.4
2019	1.4
2020	1.3
2021	1.3
2022	1.2